Signal reproducing method and device, signal recording method and device, and code sequence generating method and device

ABSTRACT

It is intended to remove a risk of illegal high quality restoration while enabling trial viewing of contents such as music, to make it possible to reproduce contents with high quality by acquiring a relatively small amount of data, and to make it possible to implement hardware at a lower cost. To generate trial listening data containing dummy data, a pseudo random number R is generated first. A remainder r of R divided by 128 is calculated. The remainder r is coded and incorporated into high sound quality restoration data. A bandwidth limitation region of trial listening data is replaced by dummy data starting from its rth bit. As a result, the head position of the dummy data in the trial listening data varies frame by frame, whereby the safety of the trial listening data can be increased.

This application claims priority to Japanese Patent Application NumbersJP2002-067481 filed Mar. 12, 2002, JP2002-107083 filed Apr. 9, 2002 andJP2002-114784 filed Apr. 17, 2002 respectively which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a signal reproducing method and device,a signal recording method and device, and a code sequence generatingmethod and device. For example, the invention relates to a signalreproducing method and device, a signal recording method and device, anda code sequence generating method and device for coding a signal so asto enable trial viewing and, if a trial viewer decides to buy an itemconcerned, enabling high-quality reproduction and recording by addingdata having a small amount of information.

2. Description of the Related Art

The application is based on and claims priority (under the ParisConvention, Article 4) from Japanese Patent Application Nos. 2002-067481(filed Mar. 12, 2002), 2002-107083 (filed Apr. 9, 2002), and 2002-114784(filed Apr. 17, 2002), the disclosures of all of which are incorporatedherein by reference in their entireties.

Because of the spread of communication network technologies such as theInternet, the improvement of information compression technologies, theincrease in the degree of integration (integration density) ofinformation recording media, and other factors, a marketing form is nowavailable in which digital contents formed by various kinds ofmultimedia data such as data of audio, a still image, a moving image, amovie consisting of audio and a moving image are delivered to viewersover communication networks with charge.

For example, stores that sell package media such as CDs (compact discs)and MDs (mini-disks)(trademark), that is, recording media on whichdigital contents are recorded in advance can sell not only package mediabut also digital contents themselves by installing there an informationterminal such as what is called an MMK (multimedia KIOSK) in which alarge number of digital contents as typified by music data are stored.

A user inserts a recording medium he brought such as an MD into the MMK,selects the title of a digital content he wants to buy by referring to amenu picture or the like, and pays for a requested price of the content.The payment method may be input of cash, use of digital money, orelectronic payment using a credit card or a prepaid card. The MMKrecords, by performing prescribed processing, the selected digitalcontent data on the recording medium the user inserted.

A marketer of digital contents can deliver digital contents to usersover the Internet, for example, as well as sell digital contents tousers using MMKs as described above.

It has become possible to distribute contents more effectively byemploying the above-described method of marketing not only package mediaon which contents are recorded in advance but also digital contentsthemselves.

JP-A-2001-103047, JP-A-2001-325460, etc. disclose techniques that enabledistribution of digital contents while protecting its copyright. Thesetechniques make it possible to deliver a digital content in such amanner that portions other than a portion for trial listening areencrypted and allow only a user who has bought a corresponding decodingkey to listen to all the content. One known encryption method is suchthat an encrypted bit string is obtained by EXCLUSIVE-ORing PCM (pulsecode modulation) digital audio data to be delivered with a 0/1 randomnumber series generated by giving an initial value of a random numberseries as a key signal for the bit string of the PCM data. Digitalcontents that have been encrypted in this manner are distributed tousers in a manner that they are recorded on recording media by usingMMKs or the like and delivered over networks. A user who has acquiredencrypted digital content data can listens to only a non-encrypted,trial-allowed portion unless he gets a key. The user receives only noiseif he reproduces an encrypted portion without decoding it.

As described above, the encryption method is known in which a bit stringobtained by EXCLUSIVE-ORing the bit string of a PCM acoustic signal witha 0/1 random number series generated by giving initial values of arandom number series as a key signal for the bit string of the PCMacoustic signal is transmitted or recorded on a recording medium. Thismethod makes it possible to allow only a person who has acquired the keysignal to reproduce the acoustic signal correctly and to cause a personwho has not acquired the key signal to be able to reproduce only noise.Naturally, it is possible to use, as an encryption method, a morecomplex method such as what is called DES (data encryption standard).The content of the DES is disclosed in Federal Information ProcessingStandards Publication 46, Specifications for the DATA ENCRYPTIONSTANDARD, Jan. 15, 1977.

Incidentally, methods for broadcasting an audio signal after compressingit or recording an audio signal on a recording medium are spread andmagneto-optical discs capable of recording a coded audio, speech, orlike signal are used widely.

Various methods for high-efficiency coding of audio data are known,examples of which are subband coding (SBC) in which an audio signal onthe time axis is coded by dividing it into a plurality of frequencybands without dividing it into blocks and blocked frequency banddivision coding (what is called transform coding) in which a signal onthe time axis is spectrum-converted into a signal on the frequency axiswhich is then divided into a plurality of frequency bands and coded on aband-by-band basis. Another method is available in which a signal issubjected to subband coding and a resulting signal in each band isspectrum-converted into a signal on the frequency axis and coded in eachspectrum conversion band.

Among filters used in the above methods is a QMF (quadrature mirrorfilter), which is disclosed in R. E. Crochiere: “Digital Coding ofSpeech in Subbands,” Bell Syst. Tech. J., Vol. 55, No. 8, 1974. JosephH. Rothweiler: “Polyphase Quadrature Filters—A New Subband CodingTechnique,” ICASSP 83, Boston, for example, discloses a filter divisiontechnique using filters having the same bandwidth.

An example of the above-mentioned spectrum conversion is a method inwhich an input audio signal is blocked into unit frames of apredetermined duration and is subjected to discrete Fourier transform(DFT), discrete cosine transform (DCT), modified DCT transform (MDCT),or the like on a unit frame basis. The details of MDCT are described inJ. P. Princen, A. B. Bradley (Univ. of Surrey Royal Melbourne Inst. ofTech.), et al., “Subband/Transform Coding Using Filter Band DesignsBased on Time Domain Aliasing Cancellation,” ICASSP 1987.

Where the above-mentioned DFT or DCT is used as a method forspectrum-converting a waveform signal, if transform is performed foreach time block including M samples, M independent real number data areobtained for each block. To reduce distortion due to connection betweenadjoining time blocks, adjoining blocks are usually overlapped with eachother by N/2 samples; each block has N overlap samples (N/2 samples oneach side). Therefore, in DFT or DCT, on average, M independent realnumber data are quantized and coded for M+N samples.

In contrast, where the above-mentioned MDCT is used as a spectrumconversion method, if transform is performed for each time blockincluding M samples, M independent real number data are obtained from 2Msamples because each block is overlapped with each of the two adjacentblocks by M/2 samples (M samples in total). Therefore, in MDCT, onaverage, M independent real number data are quantized and coded for Msamples.

In a decoding device, a waveform signal can be reconstructed bycombining together waveform components, while interfering with eachother, obtained by inverse-converting individual blocks of a codesequence that was generated by using MDCT.

In general, the frequency resolution of a spectrum is increased andenergy is concentrated in a particular spectrum component by elongatingthe transform time block. By performing transform using MDCT in whichtransform is performed for a long block that is overlapped with each ofthe adjacent blocks by a half of its length and the number of resultingspectrum signals is not greater than the number of original time-domainsamples, coding can be made more efficient than in the case of using DFTor DCT. Inter-block distortion of a waveform signal can be reduced bygiving a sufficiently long overlap to adjoining blocks.

Bands where quantization noise occurs can be controlled by quantizing asignal that has been divided into bands by filtering or spectrumconversion in the above-described manner, and more efficient coding canbe performed for the human auditory sense by utilizing such features asa masking effect. Even more efficient coding can be performed by, forexample, normalizing a signal component of each band by a maximum valueof its absolute values before performing quantization.

In quantizing each of frequency components obtained by frequency banddivision, the frequency division widths may be determined by, forexample, taking into consideration the properties of the human auditorysense. That is, an audio signal may be divided into a plurality of bands(e.g., 25 bands) in such a manner that the bandwidth becomes greater asthe frequency increases (the highest frequency band is generally calleda critical band).

Where band division is performed so as to produce a wide critical band,data in respective bands may be coded in such a manner that prescribednumbers of bits may be assigned to the respective bands or the numbersof bits to be allocated to the respective bands may be determinedadaptively.

For example, when coefficient data obtained by MDCT are coded with bitallocation, the numbers of bits to be allocated and to be coded to MDCTcoefficient data in respective bands that are obtained by block-by-blockMDCT are determined adaptively. For example, the following two bitallocation methods are known.

R. Zelinski, P. Noll, et. al.: “Adaptive Transform Coding of SpeechSignals,” IEEE, Transactions of Acoustics, Speech, and SignalProcessing, Vol. ASSP-25, No. 4, August 1977 describes a method in whichbit allocation is performed on the basis of the signal magnitude in eachband. This method can produce a flat quantization noise spectrum andminimize the noise energy. However, since the masking effect is notutilized when the auditory sense is taken into consideration, thismethod is not an optimum one in terms of reducing noise that can beheard actually by the human ear.

M. A. Kransner (Massachusetts Institute of Technology): “The CriticalBand Coder Digital Encoding of the Perceptual Requirements of theAuditory System,” ICASSP 1980 describes a method in which fixed bitallocation is performed by obtaining signal-to-noise ratios necessaryfor respective bands by utilizing auditory masking. However, because ofthe fixed bit allocation, characteristic values are not very good evenin the case where a characteristic is measured with input of a sinewave.

To solve the above problems, a high-efficiency coding device has beenproposed in which all bits that can be used for bit allocation aredivided into bits for a fixed bit allocation pattern that ispredetermined for each small block and bits for bit allocation dependingon the signal size of each block and the division ratio is determineddepending on a signal relating to an input signal in such a manner thatthe bits for a fixed bit allocation pattern is given a larger proportionas that signal has a smoother spectrum.

Where the energy is concentrated in a particular spectrum component asin the case of sine wave input, this method can greatly increase thetotal signal-to-noise ratio because a large number of bits can beallocated to a block including the particular spectrum component. Ingeneral, the human auditory sense is very sensitive to a signal having asteep spectrum component. Therefore, increasing the signal-to-noiseratio by such a method is effective in improving not only measuredcharacteristic values but also the quality of sound actually heard by aperson.

Other various bit allocation methods have been proposed. Sophisticatedmodels of the auditory sense and improvement in the ability of codingdevices have made it possible to not only obtain better measuredcharacteristic values but also perform higher-efficiency coding for thehuman auditory sense. In these methods, in general, bit allocationreference values (real numbers) that realize a calculatedsignal-to-noise-characteristic as faithfully as possible are determinedand integers as their approximations are determined and set as thenumbers of bits to be allocated.

Japanese Patent Application No. 152865/1993 or WO 94/28633 of thepresent inventors describes a method in which tone components that areparticularly important in terms of the auditory sense, that is,components whose energy is concentrated in the neighborhood of aparticular frequency, are separated from generated spectrum signals andcoded separately from the other spectrum components. This method makesit possible to code an audio signal or the like effectively at a highcompression ratio while causing almost no deterioration for the humanauditory sense.

In generating an actual code sequence, quantization accuracy informationand normalization coefficient information are coded with a prescribednumber of bits in each band where normalization and quantization areperformed and then normalized and quantized spectrum signals are coded.ISO/IEC 11172-3 (1993(E), 1993) describes a high-efficiency codingmethod in which the number of bits for representing quantizationaccuracy information is set so as to vary from one band to anotherdepending on a band. More specifically, according to this standard, thenumber of bits for representing quantization accuracy informationdecreases as the band becomes higher in frequency.

A method is known in which quantization accuracy information isdetermined based on normalization coefficient information, for example,in a decoding device instead of coding quantization accuracy informationdirectly. However, in this method, the relationship betweennormalization coefficient information and quantization accuracyinformation is determined at the time of establishment of a standard,and hence it is impossible to introduce, in the future, a control thatemploys quantization accuracy that is based on a more advanced auditorymodel. Further, where compression ratios in a certain range are to berealized, it is necessary to set a relationship between normalizationcoefficient information and quantization accuracy information for eachcompression ratio.

A method for performing coding efficiently using variable-length codesthat is disclosed in D. A. Huffman: “A Method for Construction ofMinimum Redundancy Codes,” Proc. I.R.E., Vol. 40, p. 1,098, 1952, forexample, is known as a method for coding quantized spectrum signals moreefficiently.

It is also possible to distribute a signal that has been coded by any ofthe above-described methods by encrypting it in the same manner as inthe case of a PCM signal. Where this scrambling method is employed, aperson who has not acquired a key signal cannot reproduce an originalsignal. Another method is known in which a PCM signal is converted intoa random signal and then coded for compression instead of encrypting acoded bit sequence. However, where this scrambling method is employed, aperson who has not acquired a key signal can reproduce only noise.

The marketing of contents data can be promoted by distributing triallistening data of the contents data. Examples of trial listening dataare data that are reproduced with lower sound quality than original dataand data that enables reproduction of part (e.g., a climax portion) oforiginal data. If a user likes reproduced trial listening data, heattempts to buy a decryption key to enable reproduction of the originalsound or to buy a new recording medium on which the original audio dataare recorded.

However, with the above scrambling methods, none of the data cannot bereproduced or all the data are reproduced as noise. Therefore, the abovescrambling methods cannot be used for the purpose of distribution, fortrial listening, of a recording medium on which sound is recorded withrelatively low quality. Even if data that have been scrambled by any ofthe above methods are distributed to a user, he cannot recognize anoutline of the entire data.

In the conventional methods, in encrypting a signal that has beensubjected to high-efficiency coding, it is usually very difficult forcommon reproducing devices to produce a meaningful code sequence whilenot lowering the compression efficiency. That is, where a code sequencegenerated by high-efficiency coding is scrambled in the above describedmanner, only noise is generated if the code sequence is reproducedwithout descrambling it. If a scrambled code sequence does not complywith the standard of original high-efficiency codes, reproductionprocessing may not be performed at all.

Conversely, where high-efficiency coding is performed after a PCM signalis scrambled, such coding becomes irreversible if the amount ofinformation is reduced by utilizing the properties of the auditorysense. Therefore, even if such high-efficiency codes are decoded, ascrambled PCM signal cannot be reproduced correctly. That is, it is verydifficult to descramble such a signal correctly.

Therefore, conventionally, a method that allows correct descramblingthough lowers the compression efficiency is employed.

In view of the above problems, the present inventors proposed, inJP-A-10-135944, an audio coding method in which data obtained byencrypting only codes corresponding to high-frequency bands among codesobtained by converting music data, for example, into spectrum data aredistributed as trial listening data so that even a user not having a keycan decode and reproduce a non-encrypted, narrow-band signal. In thismethod, high-frequency-side codes are encrypted, high-frequency-side bitallocation information is replaced by dummy data, and truehigh-frequency-side bit allocation information is recorded at suchpositions that a reproduction decoder does not read (i.e., disregards)information during reproduction processing.

This method allows a user to have trial listening data distributed,reproduce those data, buy a chargeable key for decoding trial listeningdata he likes into original data, and enjoy desired music or the likewith high sound quality by reproducing it correctly in all bands.

According to the technique disclosed in JP-A-10-135944, a user nothaving a key can decode only a narrow-band signal of data that aredistributed free of charge. However, the safety relies on only theencryption. Therefore, if the encryption is cracked, a user canreproduce music with high sound quality without paying a charge. Thedistributor of music data (contents provider) cannot collect alegitimate charge.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances,and an object of the invention is therefore to provide a signalreproducing method and device, a signal recording method and device, anda code sequence generating method and device which make it possible toeliminate a possibility of encryption cracking without encrypting partof a signal while enabling trial viewing, to enable high-quality signalreproduction merely by acquiring a relatively small amount of additionaldata for a signal that is supplied for trial viewing, and to increasethe safety of trial viewing data by making difficult the act itself ofobtaining information on the additional data.

Another object of the invention is to make it possible to generate anddistribute trial listening data that enable low-sound-qualityreproduction of contents data, to restore original data from such triallistening data, and to provide very safe trial listening data from whichit is difficult to reproduce original data illegally.

According to a first aspect of the invention, trial viewing data aregenerated by replacing, with dummy data, frame by frame, part of a codesequence obtained by coding a signal in units of a frame, and theposition of the dummy data is varied. Information indicating the dummydata position is incorporated into high quality restoration data.

The present assignee proposed a technique in which data (trial viewingdata) obtained by replacing part of a code sequence with dummy data aredistributed to enable trial viewing and users are allowed to freelyreproduce sound and video of a narrow band and relatively low quality.If a trial viewer has decided to buy the item because he likes itscontents, he can receive correct data (high quality restoration data) toreplace the dummy data and enjoy its reproduction with high quality. Inthis technique, a music signal is converted into spectrum coefficientsfor each block having a prescribed length, the spectrum coefficients aredivided into tone components and the other components, and the tonecomponents are normalized and re-quantized individually and the othercomponents are normalized and re-quantized for each prescribed band.When spectrum signals obtained by the re-quantization are coded from thelow-frequency side by using variable-length codes, normalizationcoefficients of parts of the tone components and the other componentswhose frequencies are higher than a prescribed frequency are replaced bydummy data and a low-frequency-side portion of part of thevariable-length-coded spectrum components whose frequencies are higherthan the prescribed frequency is also replaced by dummy data.Reproduction of a wide-band music signal is enabled by acquiring anadditional data sequence to be used for dummy data replacement andcombining it with dummy-data-inclusive trial listening data that aregenerated in-the above manner. In this technique, an important factorfor increasing the safety is the length over which a low-frequency-sideportion of part of the variable-length-coded spectrum components whosefrequencies are higher than the prescribed frequency is replaced bydummy data. Where a spectrum code sequence of N bits is replaced bydummy data, it is possible to produce 2^(N) kinds of code sequences.Therefore, the safety, that is, the ability of preventing restoration ofcorrect data from trial listening data, can be increased by increasingN. However, increasing N leads to an increase in the amount of highquality restoration data, which means that more time is needed todownload high-quality data when a trial listener has decided to buythose data.

In view of the above, according to the first aspect of the invention,the position from which a variable-length code sequence of the abovekind is replaced by dummy data is made variable and informationindicating that position is incorporated in high quality restorationdata. This makes it possible to provide a large number of kinds of datato be checked in inferring high-quality data from trial viewing dataeven with a relatively small N value. The safety of the trial viewingdata can be increased while the size of high quality restoration data iskept relatively small.

The first aspect of the invention provides a signal reproducing methodand device for reproducing a code sequence obtained by coding a signalin prescribed units (e.g., in units of a frame) in which a first codesequence obtained by replacing part of the code sequence with dummy datais received, if a second code sequence containing information necessaryfor dummy data replacement is received, at least part of the dummy dataof the first code sequence are replaced by true data by using the secondcode sequence, and the first code sequence or a resulting code sequenceis decoded. The position of the dummy data in the first code sequence isvariable in the prescribed units.

The first aspect of the invention also provides a signal recordingmethod and device for recording, on a recording medium, a code sequenceobtained by coding a signal in units of a frame in which a first codesequence obtained by replacing part of the code sequence with dummy datais received, and if a second code sequence containing informationnecessary for dummy data replacement is received, at least part of thedummy data of the first code sequence are replaced by true data by usingthe second code sequence. The position of the dummy data in the firstcode sequence is variable. In other words, a replacement position of thedummy data can be controlled or changed in each of the prescribed units.It is noted that a head of the replacement position of the dummy data,length of the dummy data or the like can be controlled or changed ineach of the prescribed units.

The first aspect of the invention further provides a code sequencegenerating method and device in which a code sequence of a prescribedformat is generated by coding an input signal, a first code sequence isgenerated by replacing part of the code sequence of the prescribedformat with dummy data, and a second code sequence is generated byextracting the part of code sequence of the prescribed formatcorresponding to the dummy data. The position of the dummy data in thefirst code sequence is variable.

The code sequence may be generated by coding an input signal in such amanner that the input signal is spectrum-converted and divided intobands, and a code sequence having a prescribed format is generated thatcontains quantization accuracy information, normalization coefficientinformation, and spectrum coefficient information in each band, and thedummy data may include dummy data that correspond to at least part ofthe spectrum coefficient information. The spectrum coefficientinformation may be variable-length codes, and after converted intovariable-length codes the dummy data of the first code sequence are notlonger than coded data of original data.

According to a second aspect of the invention, a pseudo-code sequencesuch as a pseudo random number sequence is buried in an empty region oftrial viewing data obtained by replacing part of a code sequence withdummy data.

The present assignee proposed a technique in which data (trial viewingdata) obtained by replacing part of a code sequence with dummy data aredistributed to enable trial viewing and users are allowed to freelyreproduce sound and video of a narrow band and relatively low quality.If a trial viewer has decided to buy the item because he likes itscontents, he can receive correct data (high quality restoration data) toreplace the dummy data and enjoy its reproduction with high quality. Inthis technique, a music signal is converted into spectrum coefficientsfor each block having a prescribed length, the spectrum coefficients aredivided into tone components and the other components, and the tonecomponents are normalized and re-quantized individually and the othercomponents are normalized and re-quantized for each prescribed band.When spectrum signals obtained by the re-quantization are coded from thelow-frequency side by using variable-length codes, normalizationcoefficients of parts of the tone components and the other componentswhose frequencies are higher than a prescribed frequency are replaced bydummy data and a low-frequency-side portion of part of thevariable-length-coded spectrum components whose frequencies are higherthan the prescribed frequency is also replaced by dummy data.Reproduction of a wide-band music signal is enabled by acquiring anadditional data sequence to be used for dummy data replacement andcombining it with dummy-data-inclusive trial listening data that aregenerated in the above manner. In this technique, an important factorfor increasing the safety is that a low-frequency-side portion of partof the variable-length-coded spectrum components whose frequencies arehigher than the prescribed frequency is replaced by dummy data. In thismanner, reproduction of a wide-band music signal is enabled by acquiringan additional data sequence to be used for dummy data replacement andcombining it with dummy-data-inclusive trial listening data that aregenerated in the above manner.

However, in the case of a fixed bit rate, the same number of bits areallocated to each frame and, if residual bits occur as a result ofcoding, usually bits having a fixed value “0” or “1” are arranged in theregion of the residual bits. However, when someone attempts to increasethe bandwidth of trial listening data illegally by inferring avariable-length code sequence of the trial listening data, this methodmay allow him to use, as a criterion for judging whether an inferredcode sequence is a correct one, whether the inferred code sequence isclose, in length, to the correct one.

In view of the above, according to the second aspect of the invention,0s and 1s are arranged randomly in the residual bit portion of eachframe. As a result, when someone attempts to increase the bandwidth oftrial listening data illegally, it is difficult for him to judge whetheran inferred code sequence is a correct one. Therefore, increasing thebandwidth of trial listening data illegally can be prevented and hencethe safety of the trial listening data is increased.

The second aspect of the invention provides a signal reproducing methodand device for reproducing a code sequence obtained by coding a signalin prescribed units in which a first code sequence obtained by replacingpart of the code sequence with dummy data is received, if a second codesequence containing information necessary for dummy data replacement isreceived, at least part of the dummy data of the first code sequence arereplaced by true data by using the second code sequence, and the firstcode sequence or a resulting code sequence is decoded. A pseudo-codesequence such as a pseudo random number sequence is buried in an emptyregion of the first code sequence.

The second aspect of the invention also provides a signal recordingmethod and device for recording a code sequence obtained by coding asignal in prescribed units in which a first code sequence obtained byreplacing part of the code sequence with dummy data is received, and ifa second code sequence containing information necessary for dummy datareplacement is received, at least part of the dummy data of the firstcode sequence are replaced by true data by using the second codesequence. A pseudo-code sequence such as a pseudo random number sequenceis buried in an empty region of the first code sequence.

The second aspect of the invention further provides a code sequencegenerating method and device in which a code sequence is generated bycoding a signal in prescribed units, a first code sequence is generatedby replacing part of the code sequence with dummy data, and a secondcode sequence containing information necessary for dummy datareplacement is generated. A pseudo-code sequence such as a pseudo randomnumber sequence is buried in an empty region of the first code sequence.

The code sequence may be generated by coding an input signal in such amanner that the input signal is spectrum-converted and divided intobands, and a code sequence having a prescribed format is generated thatcontains quantization accuracy information, normalization coefficientinformation, and spectrum coefficient information in each band, and thedummy data may include dummy data that correspond to at least part ofthe spectrum coefficient information. In this case, the empty region inthe first code sequence may be a region following the spectrumcoefficient information. The spectrum coefficient information may bevariable-length codes, and after converted into variable-length codesthe dummy data of the first code sequence are not longer than coded dataof original data.

The code sequence may include variable-length codes and at least part ofthe dummy data may correspond to variable-length codes. The first codesequence may have a fixed length.

A data converting method according to a third aspect of the inventioncomprises a calculating step of calculating a data length of third datathat are part of second data, a data converting step of converting afirst data sequence into a second data sequence by replacing, with thesecond data, first data having the same data length as the second data,and a generating step of generating a third data sequence that isnecessary for restoring the first data sequence from the second datasequence generated by the data converting step. The calculating stepcalculates a different data length every third data. The third datasequence generated by the generating step contains the data lengthscalculated by the calculating step and the first data that are replacedby the second data by the data converting step.

The first data sequence may consist of a plurality of frames, at leasttwo of the frames may contain at least one piece of first data, and thedata length of the third data may vary from one frame containingcorresponding first data to another.

The third data sequence generated by the generating step may furthercontain position information indicating a start position of the thirddata that are contained in the second data sequence.

The data converting step may convert the first data sequence to thesecond data sequence by replacing, with the second data, at least one ofplural pieces of first data contained in the first data sequence so thatthe reproduction quality is lower when the second data sequence isreproduced than when the first data sequence is reproduced.

The data converting method may further comprise a coding step of codinginput data, and the data converting step may convert coded data,produced by the coding step, as the first data sequence into the seconddata sequence.

The first data may contain variable-length codes.

The first data may contain normalization coefficient information of thecoding processing of the coding step.

The first data may contain quantization accuracy information of thecoding processing of the coding step.

The first data may contain the number of quantization units of thecoding processing of the coding step.

The data converting method may further comprise aconversion-into-frequency-components step for converting the input datainto frequency components, and a dividing step of dividing the frequencycomponents into a first signal consisting of tone components and asecond signal excluding the first signal. The coding step may performdifferent kinds of coding processing on the first signal and the secondsignal.

The data converting method may further comprise aconversion-into-frequency-components step for converting input data intofrequency components, and a coding step of coding data of the frequencycomponents. The data converting step may convert coded data, produced bythe coding step, as the first data sequence into the second datasequence. The first data may contain spectrum coefficient information ofthe coding processing of coding the frequency components produced by theconversion-into-frequency-components step.

The second data may be data obtained by replacing at least part of thefirst data with random data.

The first data may be data having prescribed numerical values, and thesecond data may be data obtained by minimizing the numerical values ofthe first data.

The data converting method may further comprise a coding step of codinginput data, and the data converting step may convert coded data,produced by the coding step, as the first data sequence into the seconddata sequence. The second data may be such as to be shorter in datalength than the first data when the first data and the second data aredecoded.

A data converting device according to the third aspect of the inventioncomprises calculating means for calculating a data length of third datathat are part of second data, data converting means for converting afirst data sequence into a second data sequence by replacing, with thesecond data, first data having the same data length as the second data,and generating means for generating a third data sequence that isnecessary for restoring the first data sequence from the second datasequence generated by the data converting means. The calculating meanscalculates a different data length every third data. The third datasequence generated by the generating means contains-the data lengthscalculated by the calculating means and the first data that are replacedby the second data by the data converting means.

A program that is recorded on a first recording medium according to thethird aspect of the invention comprises a calculating step ofcalculating a data length of third data that are part of second data, adata converting step of converting a first data sequence into a seconddata sequence by replacing, with the second data, first data having thesame data length as the second data, and a generating step of generatinga third data sequence that is necessary for restoring the first datasequence from the second data sequence generated by the data convertingstep. The calculating step calculates a different data length everythird data. The third data sequence generated by the generating stepcontains the data lengths calculated by the calculating step and thefirst data that are replaced by the second data by the data convertingstep.

A first program according to the third aspect of the invention comprisesa calculating step of calculating a data length of third data that arepart of second data, a data converting step of converting a first datasequence into a second data sequence by replacing, with the second data,first data having the same data length as the second data, and agenerating step of generating a third data sequence that is necessaryfor restoring the first data sequence from the second data sequencegenerated by the data converting step. The calculating step calculates adifferent data length every third data. The third data sequencegenerated by the generating step contains the data lengths calculated bythe calculating step and the first data that are replaced by the seconddata by the data converting step.

A data restoring method according to the third aspect of the inventioncomprises an acquisition control step of controlling acquisition of athird data sequence containing information necessary for restoring asecond data sequence from a first data sequence, and a restoring step ofrestoring the first data sequence on the basis of the third datasequence the acquisition of which is controlled by the acquisitioncontrol step. The third data sequence contains plural pieces of firstdata necessary for restoring the first data sequence and informationindicating data lengths of plural pieces of third data that are parts ofthe respective pieces of second data. The restoring step restores thefirst data sequence by replacing the plural pieces of second datacontained in the second data sequence with the plural pieces of firstdata contained in the third data sequence. The plural pieces of thirddata have different data lengths.

The first data sequence may consist of a plurality of frames, at leasttwo of the frames may contain at least one piece of first data, and thedata length of the third data may vary frame by frame.

The first data sequence may be coded data sequence, and the first datamay contain variable-length codes.

The third data sequence the acquisition of which is controlled by theacquisition control step may further contain position informationindicating a start position of the first data to replace the seconddata.

The data restoring method may further comprise a recording control stepof controlling recording, on a prescribed recording medium, of the firstdata sequence restored by the restoring step.

The data restoring method may further comprise a decoding step ofdecoding the first data sequence restored by the restoring step.

The data restoring method may further comprise a reproduction controlstep of controlling reproduction of the first data sequence decoded bythe decoding step.

The first data sequence may be coded data sequence, and the first datamay contain normalization coefficient information.

The first data sequence may be coded data sequence, and the first datamay contain quantization accuracy information.

The first data sequence may be a coded data sequence, and the first datamay contain the number of quantization units.

The first data sequence may be a data sequence obtained throughconversion into frequency components and coding, and the first data maycontain spectrum coefficient information.

The first data may be data having prescribed numerical values, and thesecond data may be data obtained by minimizing numerical values of thefirst data.

The second data may be data obtained by replacing at least part of thefirst data with random data.

The second data may be such as to be shorter in data length than thefirst data when the first data and the second data are decoded by thedecoding step.

The restoring step may restore the first data sequence by replacing,with the first data contained in the third data sequence, the seconddata contained in the second data sequence so that the reproductionquality is higher when the first data sequence is reproduced than whenthe second data sequence is reproduced.

A data restoring device according to the third aspect of the inventioncomprises acquiring means for acquiring a third data sequence containinginformation necessary for restoring a second data sequence from a firstdata sequence, and restoring means for restoring the first data sequenceon the basis of the third data sequence acquired by the acquiring means.The third data sequence contains plural pieces of first data necessaryfor restoring the first data sequence and information indicating datalengths of plural pieces of third data that are parts of the respectivepieces of second data. The restoring means restores the first datasequence by replacing the plural pieces of second data contained in thesecond data sequence with the plural pieces of first data contained inthe third data sequence. The plural pieces of third data have differentdata lengths.

A program that is recorded on a second recording medium according to thethird aspect of the invention comprises an acquisition control step ofcontrolling acquisition of a third data sequence containing informationnecessary for restoring a second data sequence from a first datasequence, and a restoring step of restoring the first data sequence onthe basis of the third data sequence the acquisition of which iscontrolled by the acquisition control step. The third data sequencecontains plural pieces of first data necessary for restoring the firstdata sequence and information indicating data lengths of plural piecesof third data that are parts of the respective pieces of second data.The restoring step restores the first data sequence by replacing theplural pieces of second data contained in the second data sequence withthe plural pieces of first data contained in the third data sequence.The plural pieces of third data have different data lengths.

A second program according to the third aspect of the inventioncomprises an acquisition control step of controlling acquisition of athird data sequence containing information necessary for restoring asecond data sequence from a first data sequence, and a restoring step ofrestoring the first data sequence on the basis of the third datasequence the acquisition of which is controlled by the acquisitioncontrol step. The third data sequence contains plural pieces of firstdata necessary for restoring the first data sequence and informationindicating data lengths of plural pieces of third data that are parts ofthe respective pieces of second data. The restoring step restores thefirst data sequence by replacing the plural pieces of second datacontained in the second data sequence with the plural pieces of firstdata contained in the third data sequence. The plural pieces of thirddata have different data lengths.

A first data format according to the third aspect of the inventionincludes a plurality of frames that are set so as to provide lowerreproduction quality than corresponding portions of contents data do.The plurality of frames contain variable-length codes, part of thevariable-length codes are replaced by dummy data, and the data length ofpart of the dummy data varies frame by frame.

A second data format according to the third aspect of the inventionincludes plural pieces of first data to replace plural pieces of seconddata contained in trial listening data, respectively, and fourth dataindicating data lengths of the plural pieces of third data that areparts of the plural pieces of second data, respectively.

In the data converting method, the data converting device, and the firstprogram according to the third aspect of the invention, data lengths ofthird data that are parts of second data are calculated, a first datasequence is converted into a second data sequence by replacing firstdata with the second data, and a third data sequence necessary forrestoring the first data sequence from the second data sequence thusgenerated is generated. Data lengths that are different for the pluralpieces of third data are calculated. The generated third data sequencecontain the calculated data lengths and the first data that have beenreplaced by the second data.

In the data restoring method, the data restoring device, and the secondprogram according to the third aspect of the invention, a third datasequence containing information necessary for restoring a second datasequence from a first data sequence is acquired, and the first datasequence is restored on the basis of the acquired third data sequence.The third data sequence contains plural pieces of first data necessaryfor restoring the first data sequence and information indicating datalengths of plural pieces of third data that are parts of the respectivepieces of second data. The first data sequence is restored by replacingthe plural pieces of second data contained in the second data sequencewith the plural pieces of first data contained in the third datasequence. The plural pieces of third data have different data lengths.

In the invention, it is preferable to employ, for example, as a formatto be used in coding an input signal, a format in which at leastportions relating to contents data (e.g., spectrum coefficients or pixelvalue) and coding parameters necessary for decoding (e.g., quantizationaccuracy information and normalization coefficient information) aremultiplexed with each other on a code sequence. It is possible tofurther multiplex meta-information relating to contents attributionsetc., copyright management information, encryption information, etc.with the above information on the code sequence.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the general configuration of anoptical disc recording and reproducing apparatus to be used for thedescription of a first embodiment of the present invention;

FIG. 2 is a block diagram showing the general configuration of anexemplary coding device to be used for the description of the firstembodiment of the invention;

FIG. 3 is a block diagram showing a specific example of a convertingmeans of the coding device of FIG. 2;

FIG. 4 is a block diagram showing a specific example of a signalcomponents coding means of the coding device of FIG. 2;

FIG. 5 is a block diagram showing the general configuration of anexemplary decoding device to be used for the description of the firstembodiment of the invention;

FIG. 6 is a block diagram showing a specific example of an inverseconverting means 1403 of the decoding device of FIG. 5;

FIG. 7 is a block diagram showing a specific example of a signalcomponents decoding means of the decoding device of FIG. 5;

FIG. 8 illustrates a coding method to be used for the description of thefirst embodiment of the invention;

FIG. 9 illustrates an exemplary code sequence that is obtained by thecoding method of FIG. 8;

FIG. 10 illustrates another exemplary coding method to be used for thedescription of the first embodiment of the invention;

FIG. 11 is a block diagram showing an exemplary signal components codingmeans to be used for implementing the coding method of FIG. 10;

FIG. 12 is a block diagram showing an exemplary signal componentsdecoding means of a decoding device for decoding a code sequence that isobtained by the coding method of FIG. 10;

FIG. 13 shows an exemplary code sequence obtained by the coding methodof FIG. 10;

FIG. 14 shows an exemplary code sequence obtained by a coding methodaccording to the first embodiment of the invention;

FIG. 15 shows an exemplary spectrum of a reproduction signal that isobtained by reproducing the code sequence of FIG. 14;

FIG. 16 shows an exemplary spectrum of a reproduction signal that isobtained by reproducing a code sequence obtained by another version ofthe coding method according to the first embodiment of the invention;

FIG. 17 shows the general configuration of a reproducing devicecorresponding to the coding method according to the first embodiment ofthe invention;

FIG. 18 shows exemplary information to replace dummy data in a codesequence obtained by the coding method according to the first embodimentof the invention;

FIG. 19 is a block diagram showing the general configuration of arecording device according to the first embodiment of the invention;

FIG. 20 shows exemplary information to replace dummy data in a codesequence obtained by the coding method according to the first embodimentof the invention;

FIG. 21 is a flowchart showing a reproducing method according to thefirst embodiment of the invention;

FIG. 22 is a flowchart showing a recording method according to the firstembodiment of the invention;

FIG. 23 shows an exemplary information to replace dummy data in a codesequence obtained by another coding method according to the firstembodiment of the invention;

FIG. 24 is a flowchart of a process that is executed by a code sequencegenerating device according to the first embodiment of the invention;

FIG. 25 is a block diagram of an exemplary reproducing device accordingto the first embodiment of the invention;

FIG. 26 is a block diagram of an exemplary recording device according tothe first embodiment of the invention;

FIG. 27 is a flowchart of a process for replacing dummy data with truedata for high quality restoration according to the first embodiment ofthe invention;

FIG. 28 shows an exemplary format of information containing trueinformation to replace dummy data according to the first embodiment ofthe invention;

FIG. 29 shows a specific example of the information containing trueinformation to replace dummy data according to the first embodiment ofthe invention;

FIG. 30 is a flowchart of a process for generating a trial listeningfile and a corresponding high quality sound restoration file accordingto the first embodiment of the invention;

FIG. 31 is a flowchart of a process for generating a high-sound-qualityfile by combining the trial listening file and the high quality soundrestoration file according to the first embodiment of the invention;

FIG. 32 shows an exemplary code sequence obtained by another codesequence generating method according to the first embodiment of theinvention;

FIG. 33 is a flowchart of another process for generating a triallistening file and a corresponding high quality sound restoration fileaccording to the first embodiment of the invention;

FIG. 34 is a block diagram showing the configuration of a coding deviceaccording to a second embodiment of the invention;

FIG. 35 is a block diagram showing a detailed configuration of aconverting section shown in FIG. 34;

FIG. 36 illustrates spectrum signals and quantization units;

FIG. 37 is a block diagram showing the configuration of a signalcomponents coding section shown in FIG. 34;

FIG. 38 is a graph showing tone components and non-tone components;

FIG. 39 is a block diagram showing the configuration of a tonecomponents coding section shown in FIG. 37;

FIG. 40 is a block diagram showing the configuration of a non-tonecomponents coding section shown in FIG. 37;

FIG. 41 shows a format of a frame of original data;

FIG. 42 is a block diagram showing the configuration of a triallistening data generating section shown in FIG. 34;

FIG. 43 shows a format of a trial listening frame;

FIG. 44 shows spectrum signals corresponding to the trial listeningframe of FIG. 43;

FIG. 45 shows a trial listening frame in which part of spectrumcoefficients are replaced by dummy data;

FIG. 46 illustrates an additional frame;

FIG. 47 is a flowchart of a trial listening data generating process;

FIG. 48 illustrates an original data frame that is generated in the casewhere tone components are not separated;

FIG. 49 illustrates trial listening data that are generated in the casewhere tone components are not separated;

FIG. 50 illustrates an additional frame that is generated in the casewhere tone components are not separated;

FIG. 51 is a block diagram showing the configuration of a datareproducing device according to the second embodiment of the invention;

FIG. 52 is a block diagram showing the configuration of a signalcomponents decoding section shown in FIG. 51;

FIG. 53 is a block diagram showing the configuration of a tonecomponents decoding section shown in FIG. 52;

FIG. 54 is a block diagram showing the configuration of a non-tonecomponents decoding section shown in FIG. 52;

FIG. 55 is a block diagram showing the configuration of an inverseconverting section shown in FIG. 51;

FIG. 56 is a flowchart of a data reproducing process;

FIG. 57 is a flowchart of a code sequence restoring process;

FIG. 58 is a block diagram showing the configuration of a data recordingdevice according to the second embodiment of the invention;

FIG. 59 is a flowchart of a data recording process; and

FIG. 60 is a block diagram showing the configuration of a personalcomputer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

Before description of a first embodiment, an optical disc recording andreproducing apparatus as a general compressed data recording andreproducing apparatus to be used for the description of the firstembodiment will be described with reference to drawings.

FIG. 1 is a block diagram of an exemplary optical disc recording andreproducing apparatus. In the apparatus of FIG. 1, a magneto-opticaldisc 1 that is rotationally driven by a spindle motor 51 is used as arecording medium. To record data on the magneto-optical disc 1, amodulated magnetic field corresponding to recording data is applied tothe disc 1 by a magnetic head 54 in a state that laser light is appliedto the disc 1 by an optical head 53, whereby data are recorded along therecording track of the magneto-optical disc 1 by what is calledmagnetic-field-modulated recording. To reproduce recorded data, therecording track of the magneto-optical disc 1 is traced by laser lightthat is emitted from the optical head 53 (magneto-optical reproduction).

For example, the optical head 53 is composed of optical parts includinga laser light source such as a laser diode, a collimator lens, an objectlens, a polarizing beam splitter, and a cylindrical lens, aphotodetector having a light receiving portion of a prescribed pattern,and other components. The optical head 53 is opposed to the magnetichead 54 with the magneto-optical disc 1 interposed in between. To recorddata on the magneto-optical disc 1, the magnetic head 54 is driven by arecording-system head driving circuit 66 (described later) so as toapply a modulated magnetic field corresponding to recording data to thedisc 1 and laser light is applied to a target track of the disc 1 by theoptical disc 53, whereby thermo-magnetic recording is performed by themagnetic field modulation method. The optical head 53 detects reflectionlight of laser light applied to a target track, and thereby detects afocusing error and a tracking error by, for example, what is called anastigmatic method and a push-pull method, respectively. To reproducedata from the magnet-optical disc 1, the optical head 53 generates areproduction signal by detecting a difference between polarizationangles (Kerr rotation angles) of reflection laser light beams comingfrom a target track while detecting a focusing error and a trackingerror.

An output of the optical head 53 is supplied to an RF circuit 55. The RFcircuit 55 extracts the focusing error and the tracking error from theoutput of the optical head 53 and supplies those signals to a servocontrol circuit 56. Further, the RF circuit 55 binarizes a reproductionsignal and supplies a resulting signal to a reproduction-system decoder71 described later.

For example, the servo control circuit 56 is composed of a focusingservo control circuit, a tracking servo control circuit, a spindle motorservo control circuit, a sled servo control circuit, etc. The focusingservo control circuit performs a focusing control on the optical systemof the optical head 53 so as to make the focusing error zero. Thetracking servo control circuit performs a tracking control on theoptical system of the optical head 53 so as to make the tracking errorzero. The spindle motor servo control circuit controls the spindle motor51 so as to rotate the magnet-optical disc 1 at a prescribed rotationspeed (e.g., at a constant linear velocity). The sled servo controlcircuit moves the optical head 53 and the magnetic head 54 to a targettrack position on the magneto-optical disc 1 that is specified by asystem controller 57. The servo control circuit 56, which performs theabove various control operations, sends, to the system controller 57,information indicating operation states of the individual componentsthat are controlled by the servo control circuit 56.

A key input manipulation section 58 and a display section 59 areconnected to the system controller 57. The system controller 57 controlsthe recording system and the reproduction system on the basis ofmanipulation input information coming from the key input manipulationsection 58. Further, the system controller 57 manages a recordingposition or a reproducing position on the recording track being tracedby the optical head 53 and the magnetic head 54 on the basis ofsector-by-sector address information that is reproduced from therecording track of the magneto-optical disc 1 as a header time, sub-codeQ data, etc. Still further, the system controller 57 performs a controlfor displaying a reproduction time on the display section 59 on thebasis of a data compression ratio of this compressed data recording andreproducing apparatus and information indicating the reproducingposition on the recording track.

In the reproduction time display, actual time information is calculatedby multiplying sector-by-sector address information (absolute timeinformation) that is reproduced from the recording track of themagneto-optical disc 1 as a header time, what is called sub-code Q data,etc. by the reciprocal of the data compression ratio (for example, it isequal to 4 if the data compression ratio is 1/4), and is displayed onthe display section 59. Also in recording, if absolute time informationis recorded in advance on the recording track of the magneto-opticaldisc 1 (i.e., the disc 1 is preformatted), a present position can bedisplayed in the form of an actual recording time by readingpreformatted absolute time information and multiplying it by thereciprocal of the data compression ratio.

In the recording system of the optical disc recording and reproducingapparatus of FIG. 1, an analog audio input signal A_(IN) that is inputfrom an input terminal 60 is supplied to an A/D converter 62 via alow-pass filter 61. The A/D converter 62 quantizes the analog audioinput signal A_(IN). A digital audio signal that is output from the A/Dconverter 62 is supplied to an ATC (adaptive transform coding) encoder63. A digital audio input signal D_(IN) that is input from an inputterminal 67 is supplied to the ATC encoder 63 via a digital inputinterface circuit 68. The ATC encoder 63 performs bit compression (datacompression) corresponding to a prescribed data compression ratio on thedigital audio PCM data having a prescribed transfer rate that has beenobtained by quantizing the input signal A_(IN) with the A/D converter62. Compressed data (ATC data) that are output from the ATC encoder 63are supplied to a memory (RAM) 64. If the data compression ratio isequal to 1/8, for example, the data transfer rate at this point isreduced to 1/8 (9.375 sectors/sec) of a data transfer rate (75sectors/sec) of what is called a CD-DA format, which is the format ofthe standard digital audio CD.

Data writing and reading on the memory (RAM) 64 are controlled by thesystem controller 57. The memory 64 serves as a buffer memory fortemporarily storing ATC data that are supplied from the ATC encoder 63and for allowing their recording on the disc 1 when necessary. That is,where the data compression ratio is equal to 1/8, for example, the datatransfer rate of compressed audio data that are supplied form the ATCencorder 63 is reduced to 1/8 (9.375 sectors/sec) of the data transferrate (75 sectors/sec) of the standard CD-DA format, which is the formatof the standard digital audio CD. Such compressed data are written tothe memory 64 consecutively. As described above, for such compresseddata (ATC data), it is sufficient to perform recording on one sector foreach set of eight sectors. However, since performing recording everyeight sectors is almost impossible in practice, sector-continuousrecording (described below) is performed.

This type of recording is performed in a burst-like manner at the samedata transfer rate (75 sectors/sec) as in the standard CD-DA format inunits of a cluster consisting of a prescribed number of sectors (e.g.,32 sectors plus several sectors) with insertion of halt periods. Thatis, ATC audio data (recording data) having the data compression ratio1/8 that were written to the memory 64 consecutively at the low transferrate of 9.375 (75/8) sectors/sec corresponding to the above-mentionedbit compression rate are read from the memory 64 in a burst-like mannerat a transfer rate of 75 sectors/sec. Although the transfer rate,including recording halt periods, of data that are read from the memory64 and will be recorded in the disc 1 is as low as 9.375 sectors/sec,the instantaneous data transfer rate during each burst-like recordingoperation is equal to the standard value of 75 sectors/sec. Therefore,if the disc rotation speed (constant linear velocity) is the same as inthe standard CD-DA format, recording is performed at the same recordingdensity with the same recording pattern as in the standard CD-DA format.

ATC audio data (recording data) that are read from the memory 64 in aburst-like manner at the (instantaneous) transfer rate of 75 sectors/secare supplied to an encoder 65. In a data sequence that is supplied fromthe memory 64 to the encoder 65, the unit of one continuous recordingoperation is a cluster consisting of a plurality of sectors (e.g., 32sectors) plus several sectors for cluster connection that are providedbefore and after the cluster, respectively. Each set of sectors forcluster connection is set longer than an interleave length of theencoder 65 so as not to affect data of other clusters even ifinterleaving is performed.

The encoder 65 performs error correction coding processing (addition ofa parity bit and interleaving) and EFM coding processing on recordingdata that are supplied from the memory 64 in a burst-like manner.Resulting recording data are supplied to the magnetic head drivingcircuit 66. The magnetic head driving circuit 66, to which the magnetichead 54 is connected, drives the magnetic head 54 so that the magnetichead 54 applies a modulated magnetic field corresponding to therecording data to the magneto-optical disc 1.

The system controller 57 performs the above-described memory control onthe memory 64, and controls recording positions so that recording datathat are read from the memory 64 in a burst-like manner under the abovememory control are recorded continuously on the recording track of themagneto-optical disc 1. The recording position control is performed insuch a manner that the system controller 57 manages recording positionsof recording data that are read from the memory 64 in a burst-likemanner and supplies the servo control circuit 56 with a control signalthat specifies recording positions on the recording tracks of themagneto-optical disc 1.

Next, the reproduction system of the optical disc recording andreproducing apparatus of FIG. 1 will be described. This reproductionsystem is to reproduce recording data that were recorded continuously onthe recording track of the magneto-optical disc 1 by the above-describedrecording system. The reproduction system is provided with a decoder 71that is supplied, after being binarized by the RF circuit 55, with areproduction output obtained by tracing the recording track of themagneto-optical disc 1 with laser light that is emitted from the opticalhead 53. The reproduction system can read not only the magneto-opticaldisc but also optical discs dedicated to reproduction of the same kindas the CD (compact disc) and what is called the CD-R optical disc.

The decoder 71, which corresponds to the encoder 65 of the recordingsystem, performs such processing as error correction decoding processingand EFM decoding processing on a reproduction output as binarized by theRF circuit 55, and reproduces ATC audio data having the data compressionratio 1/8 at a transfer rate of 75 sectors/sec which is higher than theregular transfer rate. The reproduction data produced by the decoder 71are supplied to a memory (RAM) 72.

Data writing and reading on the memory (RAM) 72 are controlled by thesystem controller 57. Reproduction data that are supplied from thedecoder 71 at the transfer rate of 75 sectors/sec are written to thememory 72 in a burst-like manner at the same transfer rate of 75sectors/sec. Reproduction data that were written to the memory 72 in aburst-like manner at the transfer rate of 75 sectors/sec are read fromit consecutively at a transfer rate of 9.375 sectors/sec whichcorresponds to the data compression ratio 1/8.

The system controller 57 performs a memory control for writingreproduction data to the memory 72 at the transfer rate of 75sectors/sec and-reading the reproduction data from the memory 72consecutively at the transfer rate of 9.375 sectors/sec. In addition toperforming the above memory control on the memory 72, the systemcontroller 57 controls reproduction positions so that reproduction datato be written to the memory 72 in a burst-like manner under the abovememory control are reproduced continuously from the recording track ofthe magneto-optical disc 1. The reproduction position control isperformed in such a manner that the system controller 57 managesreproduction positions of reproduction data to be written to the memory72 in a burst-like manner and supplies the servo control circuit 56 witha control signal that specifies reproduction positions on the recordingtrack of the magneto-optical disc (or optical disc) 1.

ATC audio data (reproduction data) that are read from the memory 72consecutively at a transfer rate of 9.375 sectors/sec are supplied to anATC decoder 73. The ATC decoder 73, which corresponds to the ATC encoder63 of the recording system, reproduces digital audio data of 16 bits byexpanding (bit expansion) ATC data by a factor of 8. The digital audiodata produced by the ATC decoder 73 are supplied to a D/A converter 74.

The D/A converter 74 converts the digital audio data that are suppliedfrom the ATC decoder 73 into an analog signal, that is, an analog audiooutput signal A_(OUT), which is output from an output terminal 76 via alow-pass filter 75.

Next, high-efficiency compression coding to be performed on a signalwill be described. That is, a technique of performing high-efficiencycoding on an input digital signal such as an audio PCM signal using thetechniques of subband coding (SBC), adaptive transform coding (ATC), andadaptive bit allocation will be described with reference to FIG. 2 andfollowing figures.

FIG. 2 is a block diagram showing a specific example of a coding devicefor coding an acoustic waveform signal that will be used for thedescription of the this embodiment. In this example, an input waveformsignal 101 is converted into a signal frequency component signal 102 bya converting means 1101. Each component is coded by a signal componentscoding means 1102, and a code sequence generating means 1103 generates acode sequence 104.

FIG. 3 shows a specific example of the converting means 1101 shown inFIG. 2. Signals in two respective bands produced by a band divisionfilter 1201 are converted into spectrum signal components 221 and 222 byforward spectrum converting means 1211 and 1212 such as MDCT elements,respectively, in the respective bands. The signal 201 in FIG. 3corresponds to the signal 101 in FIG. 2, and the signals 221 and 222 inFIG. 3 correspond to the signal 102 in FIG. 2. In the converting meansof FIG. 3, the bandwidth of the signals 211 and 212 is made ½ of that ofthe signal 201, that is, the signal 201 is decimated at a ratio of 1/2.Converting means other than the one shown in FIG. 3 are conceivable. Forexample, an input signal may be converted into spectrum signals directlyby an MDCT element. DFT (discrete Fourier transform) elements or DCT(discrete cosine transform) elements may be used rather than MDCTelements. Although it is possible to divide a signal into subbandcomponents by what is called a band division filter, it is convenient toemploy the method of converting a signal into frequency components bythe spectrum conversion which can produce a lot of frequency componentswith a relatively small amount of calculation.

FIG. 4 shows a specific example of the signal components coding means1102 shown in FIG. 2. An input signal 301 is normalized in each band bya normalizing means 1301 into a signal 302, which is quantized by aquantizing means 1303 on the basis of quantization accuracy information303 that is calculated by a quantization accuracy determining means1302, whereby a signal 304 is output. The signal 301 in FIG. 4corresponds to the signal 102 in FIG. 2. The signal 304 in FIG. 4corresponds to the signal 103 in FIG. 2 and includes not only quantizedsignal components but also normalization coefficient information and thequantization accuracy information.

FIG. 5 is a block diagram showing a specific example of a decodingdevice for producing an acoustic signal on the basis of a code sequencethat is generated by the coding device of FIG. 2. In this specificexample, codes 402 of each signal component are extracted from a codesequence 401 by a code sequence decomposing means 1401. Each signalcomponent 403 is restored from the codes 402 by a signal componentsdecoding means 1402, and an acoustic waveform signal 404 is produced byan inverse converting means 1403.

FIG. 6 shows a specific example of the inverse converting means 1403shown in FIG. 5, which corresponds to the specific example (see FIG. 3)of the converting means 1101. Signals 511 and 512 in respective bandsproduced by respective inverse spectrum converting means 1501 and 1502are combined by a band combining filter 1511. Signals 501 and 502 inFIG. 6 correspond to the signal 403 in FIG. 5, and a signal 521 in FIG.6 corresponds to the signal 404 in FIG. 5.

FIG. 7 shows a specific example of the signal components decoding means1402 shown in FIG. 5. A signal 551 in FIG. 7 corresponds to the signal402 in FIG. 5, and a signal 553 in FIG. 7 corresponds to the signal 403in FIG. 5. The spectrum signal 551 is dequantized by the dequantizingmeans 1551 into a signal 552, which is de-normalized by a de-normalizingmeans 1552, whereby a signal 553 is produced.

FIG. 8 illustrates a conventional coding method that is used in thecoding device of FIG. 2. In the example of FIG. 8, spectrum signals areones obtained by the converting means of FIG. 3. In FIG. 8, the levelsof the absolute values of spectrum signals obtained by an MDCT elementare shown in dB. Each prescribed time block of an input signal isconverted into, for example, 64 spectrum signals, which are normalizedand quantized in such a manner as to be grouped into coding units ineight bands b1 to b8. Varying the quantization accuracy from one codingunit to another depending on the manner of distribution of the frequencycomponents enables coding that can minimize deterioration in soundquality and hence is efficient for the auditory sense.

FIG. 9 shows a specific example illustrating how a signal that has beencoded in the above-described manner is recorded in a recording medium.In this specific example, a fixed-length header contains a sync signalSC and the number UN of coding units is recorded at the head of eachframe. Pieces of quantization accuracy information QN are recorded afterthe header in the number UN of coding units, and pieces of normalizationcoefficient information NP are recorded thereafter in the number UN ofcoding units. Normalized and quantized spectrum coefficient informationSP is recorded thereafter. Where the frame length is fixed, an emptyregion may be formed after the spectrum coefficient information SP. Theexample of FIG. 9 corresponds to a case that the spectrum signals ofFIG. 8 are normalized and quantized. As shown in FIG. 8, the pieces ofquantization accuracy information QN are such that 6 bits are allocatedto the lowest-frequency coding unit and 2 bits are allocated to thehighest-frequency coding unit. The pieces of normalization coefficientinformation NP are such that a value “46” is allocated to thelowest-frequency coding unit and a value “22” is allocated to thehighest-frequency coding unit. For example, the pieces of normalizationcoefficient information NP are values that are in proportion to dBvalues.

It is possible to obtain higher coding efficiency than in theabove-described method. For example, the coding efficiency can beincreased by allocating relatively short code lengths to quantizedspectrum signals that occur at high frequencies and allocatingrelatively long code lengths to quantized spectrum signals that occur atlow frequencies. Further, employing a greater conversion block lengthmakes the amount of sub-information such as the quantization accuracyinformation and the normalization coefficient information relativelysmall. Since the frequency resolution is increased, the quantizationaccuracy can be adjusted more finely on the frequency axis, which leadsto increase in coding efficiency.

The specification and the drawings of Japanese patent Application No.152865/1993 or WO 94/28633 of the present inventors describe a method inwhich tone components that are particularly important in terms of theauditory sense, that is, signal components whose energy is concentratedin the neighborhood of a particular frequency, are separated fromgenerated spectrum signals and coded separately from the other spectrumcomponents. This method makes it possible to code an audio signal or thelike efficiently at a high compression ratio while causing almost nodeterioration for the human auditory sense.

FIG. 10 illustrates a coding method that uses the above method, andshows how coding is performed by separating tone components havingparticularly high levels, for example, tone components Tn1 to Tn3, fromspectrum signals. Although pieces of position information, for example,position data Pos1 to Pos3, are necessary for the respective tonecomponents Tn1 to Tn3, the spectrum signals that remain after the tonecomponents Tn1 to Tn3 have been removed can be quantized with a smallnumber of bits. Therefore, particularly efficient coding is enabled ifthis method is used for a signal in which energy is concentrated inparticular spectrum signals.

FIG. 11 shows a configuration of the signal components coding means 1102shown in FIG. 2 that is employed in the case where tone components areseparated and coded in the above-described manner. An output signal 102(i.e., a signal 601 in FIG. 11) of the converting means 1101 in FIG. 2is separated by a tone components separating means 1601 into tonecomponents (signal 602) and non-tone components (signal 603), which arecoded by a tone components coding means 1602 and a non-tone componentscoding means 1603, respectively, whereby signals 604 and 605 areproduced. Each of the tone components coding means 1602 and the non-tonecomponents coding means 1603 has the same configuration as the signalcomponents coding means of FIG. 4. However, the tone components codingmeans 1602 also codes pieces of position information of the tonecomponents.

FIG. 12 shows a configuration of the signal components decoding means1402 shown in FIG. 5 that is employed in the case of decoding a codesequence obtained by separating and coding tone components in theabove-described manner. A signal 701 in FIG. 12 corresponds to thesignal 604 in FIG. 11, and a signal 702 in FIG. 12 corresponds to thesignal 605 in FIG. 11. The signal 701 is decoded by a tone componentsdecoding means 1701 into a signal 703, which is supplied to a spectrumsignals combining means 1703. The signal 702 is decoded by a non-tonecomponents decoding means 1702 into a signal 704, which is also suppliedto the spectrum signals combining means 1703. The spectrum signalscombining means 1703 combines together the tone components (signal 703)and the non-tone components (signal 704) and thereby produces a signal705.

FIG. 13 shows a specific example illustrating how a signal that has beencoded in the above-described manner is recorded on a recording medium.In this specific example, tone components are separated and coded and aresulting code sequence is recorded between a header and quantizationaccuracy information QN. Of the tone components sequence,number-of-tone-components information TN is recorded first and data ofthe respective tone components are recorded thereafter. The data of thetone components are position information P, quantization accuracyinformation QN, normalization coefficient information NP, and spectrumcoefficient information SP. This specific example has the followingadditional features. The frequency resolution is increased by settingthe conversion block length that is used in the conversion into spectrumsignals two times greater than in the specific example of FIG. 9. Andvariable-length codes are introduced. As a result, a code sequence of anacoustic signal that is two times longer than in the specific example ofFIG. 9 is recorded in a frame of the same number of bytes.

The techniques preceding the first embodiment of the invention have beendescribed above. When applied to audio, for example, the firstembodiment of the invention is intended to allow a user to freely listento a relatively low quality audio signal as trial listening, to allow auser to listen to a relatively high quality audio signal by, forexample, buying a relatively small amount of additional data, and tobury random data in empty regions of a trial audio signal if necessary.

More specifically, in the first embodiment of the invention, as shown inFIG. 14, in contrast to the case of FIG. 9, data indicating that no bitis allocated to each of the four high-frequency-side coding units arecoded as dummy quantization accuracy data in the quantization accuracyinformation QN and normalization coefficient information 0 (minimumdata) for each of the four high-frequency-side coding units is coded asdummy normalization coefficient data in the normalization coefficientinformation NP. In this specific example, it is assumed thatnormalization coefficients have values that are in proportion to dBvalues. Since the pieces of high-frequency-side quantization accuracyinformation are made 0 in this manner, part of the spectrum coefficientinformation SP indicated by symbol “Neg” in FIG. 14 is disregardedactually. When this code sequence is reproduced by an ordinaryreproducing device, narrow-band data having a spectrum shown in FIG. 15are reproduced. This code sequence can be used as data for triallistening. Coding the dummy data as part of the normalizationcoefficient information NP makes it more difficult to performhigh-quality reproduction illegally by inferring the quantizationaccuracy information QN.

The safety can further be increased by writing dummy data in the part ofthe spectrum coefficient information SP that is disregarded. Asdescribed later, this is more effective particularly in the case wherethe spectrum coefficient information SP is coded by usingvariable-length codes, because in this case merely replacing part of thespectrum coefficient information SP with dummy data disables correctreading of data that are higher in frequency than that range.

Further, in this embodiment, the head position of the dummy data in thespectrum coefficient information is varied frame by frame, wherebyinference of the trial listening data (mentioned above) is made moredifficult and the safety of the trial listening data is therebyincreased.

Although in the above example both of part of the quantization accuracyinformation QN and part of the normalization coefficient information NPare replaced by dummy data, only one of those may be replaced by dummydata. Where only part of the quantization accuracy information QN isreplaced by dummy data (data indicating allocation of 0 bit), thenarrow-band data having the spectrum show in FIG. 15 are reproduced.Where only part of the normalization coefficient information NP isreplaced by dummy data having a value 0, reproduced data have a spectrumas shown in FIG. 16. Although the high-frequency-side spectrum is notequal to 0 in a strict sense, it can substantially be regarded as 0 interms of audibility. In the first embodiment of the invention, the term“narrow-band signal” is used as covering this case.

Which of the quantization accuracy information QN and the normalizationcoefficient information NP is partially replaced by dummy datainfluences the risk that true values are inferred and high-qualityreproduction is enabled. Replacing both of the quantization accuracyinformation QN and the normalization coefficient information NP withdummy data partially is safest because there are no data to be used forinferring the true values. Where only the quantization accuracyinformation QN is partially replaced by dummy data, the risk isrelatively high because the quantization accuracy information QN may beinferred on the basis of the normalization coefficient information NPif, for example, an original bit allocation algorithm is such that thequantization accuracy information QN is calculated on the basis ofnormalization coefficients. In contrast, the risk is lower in the casewhere only the normalization coefficient information NP is partiallyreplaced by dummy data than in the case where only the quantizationaccuracy information QN is done so. It is also possible to selectivelyreplace part of the quantization accuracy information QN or part of thenormalization coefficient information NP with dummy data depending onthe band.

As another example, part of the spectrum coefficient information SP maybe replaced by dummy data “0.” A middle-range spectrum is particularlyimportant in terms of sound quality. Therefore, the replacement schememay be such that middle-range spectrum coefficient information isreplaced by dummy data “0” and the quantization accuracy information QNand the normalization coefficient information NP are partially replacedby dummy data in a middle/high frequency range. The dummy data may notnecessarily be “0”; for example, arbitrary codes may be used that areshorter than codes representing true values when they are used invariable-length coding. In this case, a band in which dummy quantizationaccuracy information and dummy normalization coefficient information isset so as to cover a band in which part of the spectrum coefficientinformation SP is replaced by dummy data so that narrow-bandreproduction is performed correctly. In particular, wherevariable-length codes are used for coding the spectrum coefficientinformation SP, loss of part of middle-range information entirelydisables decoding of data that are higher in frequency than that range.

In any case, inferring relatively large data relating to the contents ofa signal is more difficult than decoding a relatively short key that isused in ordinary encryption; the risk of infringement of the copyrightof a song concerned, for example, is lowered. Even if dummy data of acertain song are inferred, there is no fear that the damage expands toother songs, which is in contrast to a case that a decoding method of anencryption algorithm is uncovered. The above-described method is saferalso in this respect than a case of performing particular encryption.

FIG. 17 is a block diagram showing an exemplary reproducing deviceaccording to the first embodiment of the invention, which is an improvedversion of the conventional decoding device of FIG. 5.

In FIG. 17, an input signal 801 is a code sequence (first code sequence)in which dummy data are used partially. More specifically, quantizationaccuracy information and normalization coefficient information arepartially replaced by dummy data in the entire band or in ahigh-frequency range.

The signal 801, which is a high-efficiency-coded signal in which dummydata are buried, is received via prescribed public lines (e.g., ISDN(Integrated Services Digital Network), a satellite channel, or analoglines), for example, and input to a code sequence decomposing means1801. The contents of the code sequence are decomposed by the codesequence decomposing means 1801, and a resulting signal 802 is suppliedto a code sequence rewriting means 1802. The code sequence rewritingmeans 1802 receives, via a control means 1805, as a signal 807, truequantization accuracy information, normalizing coefficient information,and middle-range spectrum coefficient information 806 that are a secondcode sequence for replacing portions corresponding to the dummy data,and replaces dummy quantization accuracy information, normalizingcoefficient information, and middle-range spectrum coefficientinformation of the signal 802 with the true ones 806. A resulting signal803 is supplied to a signal components decoding means 1803. The signalcomponents decoding means 1803 decodes the signal 803 into spectrum data804. An inverse converting means 1804 converts the spectrum data 804into time-series data 805 and thereby reproduces an audio signal.

In the configuration of FIG. 17, in a purchase mode, the truequantization accuracy information and/or normalizing coefficientinformation and middle-range spectrum coefficient information 806 toreplace the dummy data are input to the control means 1805 via the samepublic lines as the signal 801 is done. The control means 1805 replacesthe dummy data buried in the high-efficiency-coded signal 801 that isinput to the code sequence rewriting means 1802 with the truequantization accuracy information and/or normalizing coefficientinformation and middle-range spectrum coefficient information 806. Aresulting rewritten high-efficiency-coded signal 803 is input to thesignal components decoding means 1803.

As a result, a user can listen to low-sound-quality music containingdummy data in a trial listening mode, and can listen to highsound-quality music after following a prescribed purchase procedure(charging processing, authentication processing, etc.).

In the above specific example, all the dummy data are replaced by thesecond code sequence. However, the invention is not limited to such acase. Reproduction may be performed in such a manner that at least partof the dummy data are replaced by partial code sequences of the secondcode sequence. In this case, for example, the quality of trial listening(or viewing; sound quality, image quality, etc.) can be changedarbitrarily by arbitrarily changing the percentage of partial codesequences in the second code sequence.

In the above-described reproducing device, the high-efficiency-codedsignal 801 containing dummy data and the true quantization accuracyinformation and/or normalizing coefficient information and middle-rangespectrum coefficient information 806 (the second code sequence orpartial code sequences thereof) to replace the dummy data are acquiredfrom a server via the same public lines. Alternatively, they may beacquired separately in such a manner that, for example, thehigh-efficiency-coded signal 801 that contains dummy data and is largein the amount of data is acquired via a satellite channel having a hightransmission rate and the true quantization accuracy information and/ornormalizing coefficient information and middle-range spectrumcoefficient information 806 that is small in the amount of data areacquired via lines having a relatively low transmission rate such astelephone lines or ISDN. As a further alternative, the signal 801 may besupplied being recorded on a large-capacity recording medium such as aCD-ROM or a DVD (digital versatile disc)-ROM. It is understood that theabove configurations can increase the security.

Incidentally, tone components and non-tone components were described inconnection with FIG. 13. To generate a high-efficiency-coded signal,dummy data may be buried in only the quantization accuracy informationand/or the normalization coefficient information of only the tonecomponents, only the non-tone components, or both of the tone componentsand the non-tone components.

FIG. 18 shows a specific example of a format of the true information(second code sequence) of the signal 807 that is supplied from thecontrol means 1805 of FIG. 17. This true information is to change theNth frame information shown in FIG. 14 to the information shown in FIG.9. If this change is made, the reproduction sound having the spectrum ofFIG. 15 of the code sequence containing dummy data is changed to thathaving the spectrum of FIG. 8. It is assumed here that middle-rangespectrum coefficient information to be replaced by dummy data has afixed length and the replacement by dummy data starts from the head codesequence where the bandwidth limitation starts. However, the inventionis not limited to such a case. Naturally, depending on the application,middle-range spectrum coefficient information to be replaced by dummydata may be variable in length and may start at a position distant fromthe head where the bandwidth limitation starts.

FIG. 19 is a block diagram of an exemplary recording device according tothe first embodiment of the invention. In FIG. 19, an input signal 821is a first code sequence containing partially dummy data. It is assumedthat high-frequency-side quantization accuracy information,normalization coefficient information and middle-range spectruminformation are replaced by the dummy data. The contents of the firstcode sequence are decomposed by a code sequence decomposing means 1821,and a resulting signal 822 is supplied to a code sequence rewritingmeans 1822. The code sequence rewriting means 1822 receives, via acontrol means 1824, as a signal 826, true quantization accuracyinformation, normalizing coefficient information, and middle-rangespectrum coefficient information 825 that are a second code sequence,and replaces dummy quantization accuracy information, normalizingcoefficient information, and middle-range spectrum coefficientinformation of the signal 822 with the true ones 825. A resulting signal823 is supplied to a recording means 1823. The recording means 1823records the signal 823 on a recording medium. The recording medium onwhich the code sequence of the signal 824 is to be recorded may be oneon which the code sequence of the signal 821 was recorded originally.

In the recording device of FIG. 19, as in the example of FIG. 17,recording may be performed in such a manner that at least part of thedummy data are replaced by partial code sequences of the second codesequence instead of replacing all the dummy data by the second codesequence. In this case, for example, the quality of trial listening (orviewing; sound quality, image quality, etc.) can be changed arbitrarilyby arbitrarily changing the percentage of partial code sequences in thesecond code sequence. In this case, even in a trial listening mode,partial code sequences of the second code sequence are input to thecontrol means 1824 as the signal 825 and supplied to the code sequencerewriting means 1822 as the signal 826. Therefore, it is appropriate toreplace part of the dummy data that are buried in the first codesequence coming from the code sequence decomposing means 1821 with thepartial code sequences of the second code sequence and to supply aresulting signal to the recording means 1823.

The reproducing device and the recording device according to the firstembodiment of the invention have been described above. It is possible tofurther increase the safety by encrypting high-frequency-side spectrumcoefficient information in advance. To this end, the code sequencerewriting means 1802 or 1822 in FIG. 17 or 19 for replacing dummy datanot only receives true normalization coefficient information via thecontrol means 1805 or 1824 and replaces dummy data, but also decodeshigh-frequency-side data using a decoding key that is acquired also viathe control means 1805 or 1824. Reproduction or recording is performedin this manner.

FIG. 20 shows a specific example of a format of information to replacedummy data in the case where tone components are separated as shown inFIG. 10 and coding is performed as shown in FIG. 13. If the dummy dataare replaced by this information, the reproduction sound having thespectrum of FIG. 15 of the code sequence containing dummy data ischanged to that having the spectrum of FIG. 10. It is assumed here thatmiddle-range spectrum coefficient information to be replaced by dummydata has a fixed length and the replacement by dummy data starts fromthe head code sequence where the bandwidth limitation starts. However,the invention is not limited to such a case. Naturally, depending on theapplication, middle-range spectrum coefficient information to bereplaced by dummy data may be variable in length and may start at aposition distant from the head where the bandwidth limitation starts.

FIG. 21 is a flowchart of an exemplary process that is employed whenreproduction is performed by using software in a reproducing methodaccording to the first embodiment of the invention. First, at step S11,a code sequence (first code sequence) containing dummy data isdecomposed. Whether to perform high-quality reproduction is judged atstep S12. If high-quality reproduction should be performed, dummy datain the first code sequence are replaced by true data (second codesequence) for restoring a large bandwidth at step S13 and the processgoes to step S14. Otherwise, the process directly goes to step S14. Atstep S14, signal components are decoded. At step S15, inverse conversioninto a time-series signal is performed, whereby sound is reproduced.

FIG. 22 is a flowchart of an exemplary process that is employed whenrecording is performed by using software in a recording method accordingto the first embodiment of the invention. First, whether to performhigh-quality recording is judged at step S21. If high-quality recordingshould be performed, a code sequence (first code sequence) containingdummy data is decomposed at step S22. Dummy data in the first codesequence are replaced by true data (second code sequence) for restoringa large bandwidth at step S23 and the process goes to step S24, whererecording is performed. Otherwise, the process directly goes from stepS21 to step S24.

Incidentally, in the example of FIG. 20, the true middle-range spectrumcoefficient information has a fixed length. However, in the firstembodiment of the invention, as shown in FIG. 23, the entire true datafor one frame may have a fixed length. To this end, for example, thedata amount of the middle-range spectrum coefficient information isvaried in accordance with the data amount of pieces of true tonecomponent normalization coefficient information that varies in numberframe by frame. If the length of the entire true data for one frame isset to 16 bytes, for example, in the case where the true data areencrypted by DES, two DES blocks correspond to one frame; it isappropriate to perform DES block processing two times for processing ofone frame. The control is simplified because synchronization isachieved. FIG. 23 shows one-frame codes that are obtained when the trueinformation is encrypted in the above manner. The length of the entireframe is fixed and the data amount of the middle-range spectrumcoefficient information that is located at the end is variable.

In the above coding method, since the data amount of the middle-rangespectrum coefficient information is variable, the safety is lowered atportions where the amount of dummy data is small. However, since a lotof frames exist that are continuous with each other, there are frames inwhich the amount of dummy data is large. A sufficient level of safetycan be secured as a whole. The size of the true data of each frame neednot always be fixed. For example, where DES is used, if the data amount(in bytes) is an integer multiple of 8, a relatively simple control isenabled (though less simple than in the case where the data amount iscompletely fixed) by recording, at the head of the true data, amultiplication factor indicating the data amount (a multiple of 8 bytes)and performing DES decoding that number of times.

FIG. 24 is a flowchart of a process for generating true data for highquality restoration for all frames in a code sequence generating devicecorresponding to the above method. First, at step S31, a controlvariable I is set to “1.” At steps S32, S33, and S34, truetone-component-related information, true quantization-accuracy-relatedinformation, and true normalization-coefficient-related information aregenerated, respectively. At step S35, the amount of middle-rangespectrum dummy data is calculated so that the amount of information forhigh quality restoration for one frame (i.e., the data amount of asecond code sequence) becomes constant or an integer multiple of aprescribed data amount. At step S36, true middle-range-spectrum-relatedinformation is generated. At step S37, 2-block DES encryption processingis performed. At step S38, it is checked whether the frame concerned isthe last frame. If the check result is affirmative, the process isfinished. Otherwise, the control variable I is increased by “1” at stepS39 and the process returns to step S32 to perform processing for thenext frame. In this manner, according to this method, processing forgenerating true data for high quality restoration can be performed insynchronism with block encryption processing like DES processing.

FIG. 25 is a block diagram of an exemplary reproducing device accordingto the first embodiment of the invention, which is an improved versionof the reproducing device of FIG. 17. In FIG. 25, a middle-rangespectrum dummy data amount calculating means 1846 calculates the amountof middle-range spectrum dummy data for high quality restoration data(second code sequence) 846 that are sent to a control means 1845. In thehigh quality restoration data, each frame has a fixed length or a lengththat is integer times greater than a prescribed data amount. Data 847are exchanged between the control means 1845 and the middle-rangespectrum dummy data calculating means 1846. Data 848 to replace thedummy data are supplied from the control means 1845 to a code sequencerewriting means 1842. The other part of the configuration is the same asshown in FIG. 17. Means 1801–1845 and signals 841–846 in FIG. 25 are thesame as the means 1801–1805 and the signals 801–806 in FIG. 17,respectively, and hence will not be described.

FIG. 26 is a block diagram of an exemplary recording device according tothe first embodiment of the invention, which is an improved version ofthe recording device of FIG. 19. A middle-range spectrum dummy dataamount calculating means 1865 calculates the amount of middle-rangespectrum dummy data for high quality restoration data 865 that are sentto a control means 1864. In the high quality restoration data, eachframe has a fixed length. Means 1861–1864 and signals 861–865 in FIG. 26are the same as the means 1821–1824 and the signals 821–825 in FIG. 19,respectively, and hence will not be described.

FIG. 27 is a flowchart of a process, according to the first embodimentof the invention, of replacing dummy data with true data for highquality restoration for all frames. First, at step S41, a controlvariable I is set to “1.” At step S42, 2-block DES decryption isperformed. At steps S43, S44, and S45, replacements by truetone-component-related information, true quantization-accuracy-relatedinformation, and true normalization coefficient-related information areperformed, respectively. At step S46, the amount of middle-rangespectrum dummy data is calculated so that the amount of information forhigh quality restoration for one frame becomes constant. At step S47,replacement by true middle-range-spectrum-related information isperformed. At step S48, it is checked whether the frame concerned is thelast frame. If the check result is affirmative, the process is finished.Otherwise, the control variable I is increased by “1” at step S49 andthe process returns to step S42 to perform processing for the nextframe. In this manner, according to this method, replacement of dummydata by true data for restoration of high quality can be performed insynchronism with block encryption processing like DES processing.

The above description is directed to the method for allowing a user todo trial listening on trial listening data such as those of music andrestore high sound quality by, for example, buying high-sound-qualitydata if he likes the music. In the above method, one important point ishow to make true middle-range spectrum coefficient information difficultto find.

In view of the above, exemplary methods, suitable for the firstembodiment, for making true middle-range spectrum coefficientinformation difficult to find will be described below. The followingmethods may be used either individually or in combination.

FIRST EXAMPLE

One method would be to replace as much true middle-range spectrumcoefficient information as possible with dummy data. However, thesecurity can also be increased by making it difficult to find positionsof pieces of middle-range spectrum coefficient information that isactually replaced by dummy data. In this example, this is realized byvarying the position of true middle-range spectrum coefficientinformation frame by frame. Although the following description will bedirected to a case of coding spectrum coefficient information usingsafer variable-length codes, the invention can also be applied to a casethat variable-length codes are not necessarily used.

FIG. 28 shows an example in which, to realize the above concept,information indicating the head position of true middle-range spectrumcoefficient information is contained in a true information code sequenceto replace dummy data. FIG. 29 shows how the head position of truemiddle-range spectrum coefficient information is varied frame by frame.

FIG. 30 is a flowchart showing a specific example of a method, relatingto the above method, for generating a trial listening file containingdummy data and a high sound quality restoration file containinginformation to replace the dummy data while varying the head position oftrue middle-range spectrum coefficient information.

In FIG. 30, first, at step S51, a control variable I is set to “1.” Atstep S52, dummy generation processing is performed on tone spectrumcomponent normalization coefficients. Specifically, part of tonespectrum component normalization coefficients of a trial listening fileare made “0” and the corresponding true values are coded and recorded ina high sound quality restoration file. At step S53, dummy generationprocessing is performed on non-tone spectrum component normalizationcoefficients. Specifically, part of non-tone spectrum componentnormalization coefficients of the trial listening file are made “0” andthe corresponding true values are coded and recorded in the high soundquality restoration file. At step S54, a pseudo random number isgenerated as R. For example, pseudo random numbers may be generated insuch a manner that first an arbitrary 100-bit number is selected, it issquared, and then a central 100-bit number is taken from the square (thelast two steps are repeated thereafter). However, the invention is notlimited to such a case.

At step S55, the remainder of R divided by 128 is set as r (r=R %128).At step S56, r is coded and recorded in the high sound qualityrestoration file. At step S57, dummy generation processing is performedstarting from the rth bit of a bandwidth limitation region. That is, aprescribed number of bits from the rth bit of the trial listening fileare replaced by other data and the corresponding true values arerecorded in the high sound quality restoration file. It is preferablethat the pattern in which to replace the prescribed number of bits fromthe rth bit of the trial listening file be such that 0s and 1s are mixedwith each other properly to make it difficult to infer dummy datapositions; a pattern such as an all-0 pattern that allows easy inferenceof dummy data positions should be avoided. It is preferable to prevent adecoder from decoding a beginning part of the next frame past a codesequence concerned by forming dummy data by values having shorter codelengths than true data do. At step S58, it is checked whether the frameconcerned is the last frame. If the check result is affirmative, theprocess is finished. Otherwise, the control variable I is increased by“1” at step S59 and the process returns to step S52.

FIG. 31 is a flowchart shows an exemplary process for generating ahigh-sound-quality-reproducible file on the basis of a trial listeningfile and a high sound quality restoration file (both described above).

At step S61 in FIG. 31, a control variable I is set to “1 and theprocess goes to step S62.” At step S62, dummy data of tone spectrumcomponent normalization coefficients of a trial listening file arecancelled by using the values of true normalization coefficients of ahigh sound quality restoration file. At step S63, similarly, dummy dataof non-tone spectrum component normalization coefficients of the triallistening file are cancelled by using the values of true normalizationcoefficients of the high sound quality restoration file. At step S64,the value of r is read out. At step S65, dummy data from the rth bit ofa bandwidth limitation region of the trial listening file are replacedby true middle-range spectrum coefficient information of the high soundquality restoration file. At step S66, it is checked whether the frameconcerned is the last frame. If the check result is affirmative, theprocess is finished. Otherwise, the control variable I is increased by“1” at step S67 and the process returns to step S62.

Incidentally, the manner of varying, frame by frame, the position ofmiddle-range spectrum coefficient information that is replaced by dummydata and the manner of decoding are not limited to the above specificexamples. An alternative method is such that a frame number is added tothe value of r, the remainder of the value of the addition resultdivided by 128 is set as q, and a value obtained by converting the valueof q using a random number table is used in place of r. In this case,the value of q may be written to a high sound quality restoration fileand the head position of dummy data may be determined by using the samerandom number table. This makes it more difficult to find the headposition of dummy data illegally and hence increases the safety further.

Instead of using the pseudo number, a random number may be generated by,for example, applying a varying voltage to an A/D converter of lowaccuracy and collecting seven LSBs from A/D-converted data. This alsomakes it possible to increase the safety further.

Another alternative method is such that the initial value of pseudorandom numbers generated at step S54 in FIG. 30 is recorded in a highsound quality restoration file and the same calculations as performed indetermining the head position of dummy data of a trial listening file,that is, the calculations at steps S54 and S55 of FIG. 30, are performedon the decoder side in restoring high sound quality. This eliminates theneed for recording r values of respective frames in a high sound qualityrestoration file and hence can reduce the data amount of the high soundquality restoration file.

Although in the first example the head position of dummy data is variedframe by frame, the head position of dummy data may be varied everypredetermined number of frames (i.e., at a period of a plurality offrames). The number of frames itself may be varied.

SECOND EXAMPLE

One method for finding true middle-range information would be to tryevery possible candidate code sequence for a dummy data portion. And onemethod for judging whether candidate code sequences coincide with truemiddle-range information would be to check whether the former are longerthan the latter. The number of candidates for a true code sequence canbe reduced in this manner.

Usually, the empty region (hatched region) of each frame in FIG. 14 isfilled with 0s or 1s in a fixed manner according to a standard. If oneof all possible candidate code sequences reaches the portion that isconsidered the empty region, it is excluded from the candidates. Thestart position of the empty region cannot be determined exactly becausethe last portion of an actual code sequence may coincide, in value, with0s or 1s that fill up the empty region. However, for example, if theempty region is filled with 0s and trial listening data have a lastportion that is 10 consecutive 0s, a judgment can be made that it ishighly probable that the last five 0s, for example, belong to the emptyregion. Even if code sequences that are longer than such a length areexcluded from the candidates for true code sequence, the probabilitythat the exclusion is not correct is low. Therefore, there would occurfew cases that the exclusion of such code sequences from the candidatesfor true code sequence causes a problem; the risk that trial listeningdata are converted into wide-band data illegally becomes high.

To lower the above risk, in a second example, the pattern in which tofill up the empty region is made such that 0s and 1s are arrangedrandomly instead of being made an all-0 or all-1 pattern. That is, inthe second example, the empty region of trial listening data is filledwith a pseudo-code sequence such as a pseudo random number sequence. Anexemplary method for writing random data to the empty region is suchthat a pseudo random number is generated and its lower bits that are thesame in the number of bits as the empty region are written to the emptyregion. An exemplary method for generating pseudo random numbers is suchthat first an arbitrary 100-bit number is selected, it is squared, andthen a central 100-bit number is taken from the square (the last twosteps are repeated thereafter). Naturally, the method for writing randomdata to the empty region is not limited to this method. For example, arandom number may be generated by applying a varying voltage to an A/Dconverter of low accuracy and collecting LSBs from A/D-converted data bythe number of bits of the empty region. This makes it possible toincrease the safety further.

FIG. 32 shows an exemplary code sequence in which the empty region isfilled with a random arrangement of 0s and 1s as a pseudo-code sequencesuch as a pseudo random number sequence. In this example, the emptyregion is filled with a 20-bit random pseudo-code sequence. These bitsare disregarded in a decoder for decoding a trial listening file. Theother part of FIG. 32 is the same as the corresponding part of FIG. 14and hence will not be described (the items corresponding to each otherare given the same symbol).

FIG. 33 is a flowchart showing a specific example of a method, relatingto the above method, for generating a trial listening file containingdummy data and a high sound quality restoration file containinginformation to replace the dummy data while burying a pseudo-codesequence such as a pseudo random number sequence in each empty region.

In FIG. 33, first, at step S251, a control variable I is set to “1.” Atstep S252, dummy generation processing is performed on tone spectrumcomponent normalization coefficients. Specifically, part of tonespectrum component normalization coefficients of a trial listening fileare made “0” and the corresponding true values are coded and recorded ina high sound quality restoration file. At step S253, dummy generationprocessing is performed on non-tone spectrum component normalizationcoefficients. Specifically, part of non-tone spectrum componentnormalization coefficients of the trial listening file are made “0” andthe corresponding true values are coded and recorded in the high soundquality restoration file.

At step S254, dummy generation processing is performed on middle-rangespectrum data. At this step, the pattern in which to replace aprescribed number of bits from an rth bit of the trial listening filemay be such that 0s and 1s are mixed with each other properly to make itdifficult to infer dummy data positions; a pattern such as an all-0pattern that allows easy inference of dummy data positions should beavoided. It is possible to prevent a decoder from decoding a beginningpart of the next frame past a code sequence concerned by forming dummydata by values having shorter code lengths than true data do. That is,at this step, the prescribed number of bits from the rth bit of thetrial listening file are replaced by other data and the correspondingtrue values are recorded in the high sound quality restoration file. Atstep S255, a pseudo random number is generated as R. For example, pseudorandom numbers may be generated in such a manner that first an arbitrary100-bit number is selected, it is squared, and then a central 100-bitnumber is taken from the square (the last two steps are repeatedthereafter). At step S256, a lower bit sequence of R corresponding tothe empty region is set as r. At step S257, r is recorded in the emptyregion. At step S258, it is checked whether the frame concerned is thelast frame. If the check result is affirmative, the process is finished.Otherwise, the control variable I is increased by “1” at step S259 andthe process returns to step S252.

In the above-described second example, a pseudo-code sequence such as apseudo random number sequence is buried in each empty region of triallistening data (i.e., a first code sequence for trial listening).Therefore, when someone attempts to convert trial listening data intowide-band data illegally, it is difficult for him to judge whether thewide-band data are a correct code sequence. As such, converting triallistening data into wide-band data illegally becomes difficult and thesafety of the trial listening data is increased accordingly.

In the second example, a pseudo random number as a pseudo-code sequencefor making it difficult to identify an empty region of trial listeningdata is buried in each empty region. However, the invention is notlimited such a case. In the invention, other various kinds ofpseudo-code sequences can be used as long as they have a pattern thatmakes it difficult to identify an empty region. For example, a codesequence of meaningless information having a certain degree ofrandomness and a code sequence containing meaningful information such asan electronic watermark, copyright information, or reproduction controlinformation can be used as a pseudo-code sequence.

In the second example, the empty region after spectrum coefficients isused as shown in FIG. 14 etc. However, the invention is not limited tosuch a case. In the invention, other various kinds of empty regions canbe used as long as they occur in a coded bit stream after codingaccording to a prescribed coding format is performed. It is preferablethat each of those empty regions be such that once it is identifiedidentification of dummy data and inference of dummy-replaced true datacan be facilitated. This is because such a configuration can make itdifficult to convert trial listening data into high-quality dataillegally.

Although the above description is directed to the case of using an audiosignal, the invention can also be applied to the case of using an imagesignal. For example, the same processing as in the case of an audiosignal can be performed by using a dummy quantization table in whichhigh-frequency components are removed when an image signal is convertedinto blocks by two-dimensional DCT and resulting block signals arequantized by using various quantization tables and using a truequantization table containing the high-frequency components when highimage quality is restored.

It goes without saying that the methods of the first embodiment can alsobe applied to systems in which the entire code sequence is encrypted andit is reproduced while being decrypted.

Although the first embodiment is directed to the case of recording acoded bit stream on a recording medium, the invention can also beapplied to the case of transmitting a bit stream. For example, thismakes it possible to allow only listeners who have acquired truenormalization coefficients of a broadcast audio signal over the entireband to perform high-sound-quality reproduction while allowing otherlisteners to perform reproduction of relatively low sound quality thoughthey can sufficiently recognize its contents.

Second Embodiment

Next, a second embodiment of the invention will be described. Not onlywill unique features of the second embodiment be described below, butfeatures common to the first embodiment will also be described below ifnecessary. This will allow a person skilled in the art to practice theaspect of the invention that relates to the second embodiment by readingthe following description.

The second embodiment is directed to the case of receiving a digitalsignal such as an audio PCM signal and performing high-efficiency codingon it through subband coding (SBC), adaptive transform coding (ATC), andadaptive bit allocation. The adaptive transform coding is a codingmethod that is based on the discrete cosine transform (DCT) or the likeand employs adaptive bit allocation. An input signal is coded byconverting it into spectrum signals for each time block and thennormalizing the spectrum signals together for each prescribed band, thatis, dividing each signal component by a normalization coefficient thatapproximates a maximum signal component and then quantizing eachnormalized signal component with quantization accuracy that is set eachtime according to the signal properties.

FIG. 34 is a block diagram showing the configuration of a coding device2001 that receives an acoustic waveform signal and generates triallistening data.

A converting section 2011 receives an acoustic waveform signal, convertsit into signal frequency components, and outputs those to a signalcomponents coding section 2012. The signal components coding section2012 codes the received signal frequency components and outputsresulting coded signal frequency components to a code sequencegenerating section 2013. The code sequence generating section 2013generates a code sequence on the basis of the received coded signalfrequency components and outputs it to a trial listening data generatingsection 2014. The trial listening data generating section 2014 performsprescribed processing such as rewriting of normalization coefficientinformation and dummy bit substitution on the received code sequence,and thereby converts high-sound-quality-reproducible audio data(original data) into trial listening data and generates additional data(restoration data) that corresponds to the trial listening data and isto be sold to users who want reproduction of the original data.

FIG. 35 is a block diagram showing a detailed configuration of theconverting section 2011.

An acoustic waveform signal that is input to the converting section 2011is divided into two bands by a band division filter 2021, and respectivesignals are output to forward spectrum converting sections 2022-1 and2022-2. Each of the forward spectrum converting sections 2022-1 and2022-2 converts the received signal into spectrum signal components byMDCT or the like and outputs those to the signal components codingsection 2012. The signals that are input to the respective forwardspectrum converting sections 2022-1 and 2022-2 is a half, in bandwidth,of the signal that is input to the band division filter 2021, and areinput at a half rate.

It was stated above that in the converting section 2011 in FIG. 35signals in the two bands produced by the band division filter 2021 areconverted into spectrum signal components by MDCT. However, variousmethods are available as the method for converting a received signalinto spectrum signal components. For example, a received signal may beconverted into spectrum signal components by MDCT without dividing itinto bands. Alternatively, each of the forward spectrum convertingsections 2022-1 and 2022-2 may convert a received signal into spectrumsignals by DCT or DFT.

Although it is possible to divide a received signal into band componentsusing what is called a band division filter, it is preferable to performspectrum conversion by using MDCT, DCT, or DFC each of which cancalculate a lot of frequency components with a relatively small amountof calculation.

Although in FIG. 35 the input acoustic waveform signal is divided intothe two bands by the band division filter 2021, it goes without sayingthat the number of bands need not always be two. Information indicatingthe number of bands in the band division filter 2021 is supplied to thecode sequence generating section 2013 via the signal components codingsection 2012.

FIG. 36 is a graph in which the absolute values of spectrum signalsproduced by MDCT in the converting section 2011 are converted into powerlevels. An acoustic waveform signal that is input to the conversionsection 2011 is converted into 64 spectrum signals for each prescribedtime block. The spectrum signals are divided into 16 bands, for example,that are indicated by 16 solid-line rectangles [1] to [16] in FIG. 36 bythe signal components coding section 2012 by processing to be describedlater, and are then quantized and normalized for each band. The sets ofspectrum signals corresponding to the 16 respective bands, that is, thesets of spectrum signals for which quantization and normalization areperformed individually, are quantization units.

Efficient coding capable of minimizing quality deterioration of audiblecomponents is enabled by varying the quantization accuracy for eachquantization unit in accordance with the manner of distribution offrequency components.

FIG. 37 is a block diagram showing a detailed configuration of thesignal components coding section 2012. A description will be made of acase that the signal components coding section 2012 separates tonecomponents that are particularly important in terms of the auditorysense, that is, signal components of particular frequencies where energyis concentrated, from received spectrum signals and codes the tonecomponents separately from the other spectrum components.

Spectrum signals that are input from the converting section 2011 areseparated into tone components and non-tone components by a tonecomponents separating section 2031. The tone components are output to atone components coding section 2032 and the non-tone components areoutput to a non-tone components coding section 2033.

The tone components and the non-tone components will be described withreference to FIG. 38. For example, where the spectrum signals that areinput to the tone components separating section 2031 are signals shownin FIG. 38, components having particularly high power levels areseparated, as tone components 2041–2043, from non-tone components.Position data P1–P3 indicating the positions of the separated tonecomponents 2041–2043 and their frequency widths are detected and outputto the tone components coding section 2032 together with the tonecomponents 2041–2043.

For example, the tone components separation method may be a method thatis disclosed in Japanese Patent Application No. 152865/1993 or WO94/28633 of the present inventors. The tone components and the non-tonecomponents that have been separated from each other by this method arequantized with different numbers of bits by processing (described later)of the tone components coding section 2032 and the non-tone componentscoding section 2033, respectively.

The tone components coding section 2032 codes received signals withlarge numbers of quantization bits, that is, with high quantizationaccuracy. The non-tone components coding section 2033 codes receivedsignals with small numbers of quantization bits, that is, with lowquantization accuracy.

Although it is necessary to add, for each tone component, suchinformation as its position information and frequency width, it becomespossible to quantize the spectrum signals of the non-tone componentswith small numbers of bits. In particular, an acoustic waveform signalthat is input to the coding device 2001 is a signal in which energy isconcentrated in particular spectrum components, the employment of theabove method makes it possible to perform coding effectively at a highcompression ratio while causing almost no deterioration for the humanauditory sense.

FIG. 39 is a block diagram showing a detailed configuration of the tonecomponents coding section 2032 shown in FIG. 37.

A normalizing section 2051 receives tone component spectrum signals foreach quantization unit, normalizes those, and outputs normalizedspectrum signals to a quantizing section 2052. A quantization accuracydetermining section 2053 calculates quantization accuracy by referringto a received quantization unit and outputs a calculation result to thequantizing section 2052. Since the received quantization unit consistsof tone components, the quantization accuracy determining section 2053outputs high quantization accuracy. The quantizing section 2052generates codes by quantizing the normalized spectrum signals that arereceived from the normalizing section 2051 with the quantizationaccuracy that has been determined by the quantization accuracydetermining section 2053, and outputs the generated codes andcoding-related information such as normalization coefficient informationand quantization accuracy information.

The tone components coding section 2032 also codes and outputs, togetherwith the tone components, the tone components position information thatis received together with the tone components.

FIG. 40 is a block diagram showing a detailed configuration of thenon-tone components coding section 2033 shown in FIG. 37.

A normalizing section 2054 receives non-tone component spectrum signalsfor each quantization unit, normalizes those, and outputs normalizedspectrum signals to a quantizing section 2055. A quantization accuracydetermining section 2056 calculates quantization accuracy by referringto a received quantization unit and outputs a calculation result to thequantizing section 2055. Since the received quantization unit consistsof non-tone components, the quantization accuracy determining section2056 outputs low quantization accuracy. The quantizing section 2055generates codes by quantizing the normalized spectrum signals that arereceived from the normalizing section 2054 with the quantizationaccuracy that has been determined by the quantization accuracydetermining section 2056, and outputs the generated codes andcoding-related information such as normalization coefficient informationand quantization accuracy information.

It is possible to provide higher coding efficiency than provided by theabove coding method. For example, the coding efficiency can further beincreased by performing variable-length coding in such a manner thatrelatively short code lengths are allocated to quantized spectrumsignals that occur at high frequencies and relatively long code lengthsare allocated to quantized spectrum signals that occur at lowfrequencies.

The code sequence generating section 2013 in FIG. 34 generates a codesequence that can be recorded on a recording medium or transmitted toanother information processing apparatus via a data transmission line,that is, a code sequence consisting of a plurality of frames, on thebasis of codes of signal frequency components that are output from thesignal components coding section 2012, and outputs those to the triallistening data generating section 2014. The code sequence that isgenerated by the code sequence generating section 2013 is audio datathat can be reproduced by an ordinary decoder with high sound quality.FIG. 41 shows a format of a frame of audio data that are generated bythe code sequence generating section 2013 and that can be reproducedwith high sound quality.

A fixed-length header containing a sync signal is provided at the headof each frame. The header also contains such information as the numberof bands of the band division filter 2021 of the converting section 2011that was described above with reference to FIG. 35.

Each frame contains tone component information relating to separatedtone component that follows the header. The tone component informationincludes the number of tone component, tone widths, and quantizationaccuracy information of the quantization that was performed on the tonecomponent by the tone component coding section 2032 that was describedabove with reference to FIG. 39. A normalization coefficient, tonepositions, and spectrum coefficients of each of the tone components2041–2043 follow the quantization accuracy information. It is assumedthat the normalization coefficients of the tone components 2041–2043 areequal to 30, 27, and 24, respectively.

Non-tone component information follows the tone component information.The non-tone components information contains the number of quantizationunits (in this example, 16), quantization accuracy information of thequantization that was performed on the non-tone components by thenon-tone components coding section 2033 that was described above withreference to FIG. 40, pieces of normalization coefficient information ofthe 16 respective quantization units, and spectrum coefficientinformation. The normalization coefficient information is values of therespective quantization units, that is, a value “46” of thelowest-frequency quantization unit [1] to a value “8” of thehighest-frequency quantization unit [16]. It is assumed that thenormalization coefficient information is values that are in proportionto power levels (in dB) of spectrum signals. Where content frames have afixed length, an empty region may be provided after the spectrumcoefficient information.

FIG. 42 is a block diagram showing a detailed configuration of the triallistening data generating section 2014 shown in FIG. 34.

A trial data generation processing control section 2061 causes abandwidth limitation processing section 2063 to generate trial listeningframes by controlling it on the basis of setting data such as a triallistening band of trial listening data that is input from an externalmanipulation input section (not shown) and random numbers that are inputfrom a random number generating section 2062. The trial listening bandis a frequency band for low-quality reproduction. Only part of thequantization units are designated among the spectrum data of FIG. 38,for example, whereby spectrum data in only a certain range (frequencyband) are made reproducible and the quality of reproduction sound islowered. The trial data generation processing control section 2061determines, on the basis of a pseudo random number X that is suppliedfrom the random number generating section 2062, a bit length of dummydata with which the bandwidth limitation processing section 2063replaces spectrum coefficient information by processing described later.

The random number generating section 2062 generates a different pseudorandom number X every time a frame is input to the bandwidth limitationprocessing section 2063, and supplies it to the trial data generationprocessing control section 2061. For example, the random numbergenerating section 2062 generates pseudo random numbers X by selecting a100-bit arbitrary number first, squaring it, and selecting central 100bits from the square (the last two steps are repeated plural times (anarbitrary number of times)). It goes without saying that the method forgenerating pseudo random numbers X may be any method.

The bandwidth limitation processing section 2063 generates a triallistening frame by limiting the trial listening band of the receivedframe on the basis of the signal received from the trial data generationprocessing control section 2061. The information on the trial listeningband is supplied from the trial data generation processing controlsection 2061.

For example, if the quantization units [1] to [12] are designated as atrial listening band of a trial-listening-allowable portion, thebandwidth limitation processing section 2063 minimizes the values of thenormalization coefficient information of the quantization units [13] to[16] that are higher in frequency than the trial listening band to “0,”for example, as shown in FIG. 43. Therefore, although the portion of thespectrum coefficient information corresponding to the quantization units[13] to [16] has effective values, during reproduction spectrum signalsof this portion have values that are substantially equal to “0” in termsof audibility though strictly they are not “0” because the normalizationcoefficient information is “0.” Spectrum coefficient information that ishigher, in frequency, than the position indicated by symbol Ad in FIG.43 will as good as not be referred to.

As in the case of the non-tone components, the values of normalizationcoefficients out of the trial listening band of the tone components areminimized to “0,” for example, whereby during reproduction spectrumsignals of those tone components are also minimized (to valuessubstantially equal to “0”).

FIG. 44 shows spectrum signals that are obtained when the triallistening data of FIG. 43 are reproduced. Since the normalizationcoefficient information of the quantization units [13] to [16] ischanged to “0,” corresponding spectrum signals are minimized. Spectrumsignals corresponding to the two tone components that are contained inthe quantization units [13] to [16] are also minimized in a similarmanner. That is, when the trial listening data are reproduced, onlynarrow-band spectrum signals are reproduced in atrial-listening-allowable portion.

In this manner, only narrow-band data are reproduced when the triallistening data are reproduced. Therefore, data that are lower in qualitythan the original data that were described above with reference to FIG.41 are reproduced.

The bandwidth limitation processing section 2063 inserts random dummydata into the region of the spectrum coefficient information that willnot be referred to, that is, the region that will be disregarded whenthe trial listening data are reproduced because of reproduction qualityrestriction, with a data length that is calculated by the triallistening data generation processing control section 2061 and variesframe by frame (the spectrum coefficients that will not be referred toare replaced by the dummy data). FIG. 45 shows a format of a resultingframe.

In particular, where the spectrum coefficient information are givenvariable-length codes and the variable-length codes are arranged in theregion of the spectrum coefficient information in order from thelow-frequency side to the high-frequency side, part of a middle-rangevariable-length codes are lost by inserting the random dummy data intothe region of the spectrum coefficients that will not be referred towith the data length R that varies frame by frame. Therefore,high-frequency-side data including that portion cannot be decoded atall. It is very difficult to restore the spectrum coefficientinformation relating to original data that is not contained in the triallistening data without using additional data. The safety of the triallistening data is thus increased.

For example, if N bits of the spectrum coefficient information arereplaced by dummy data, 2^(N) kinds of inference data will occur ininferring true data for the dummy data of N bits.

As described above, where part of the normalization coefficients or thespectrum coefficients are replaced by “0” or dummy data, inferring truedata corresponding to the replacement data is much more difficult thandeciphering a relatively short encryption key. Illegally altering thetrial listening data may deteriorate the sound quality on the contrary.Therefore, it is very difficult for a user who is not permitted tolisten to the original data to infer the original data on the basis ofthe trial listening data; the rights of an author and a distributor ofcontents data can be protected strongly.

Should true data corresponding to replacement data of certain triallistening data be inferred successfully, the damage does not expand toother contents. Therefore, the method according to this embodiment issafer than the case of distributing, as trial listening data, contentsdata that are encrypted according to a particular algorithm.

The original values of the normalization coefficient information and thespectrum coefficient information that were changed by the bandwidthlimitation processing section 2063 (i.e., the true normalizationcoefficient information and the true spectrum coefficient information)and information indicating the start position of the dummy data thatreplaced part of the spectrum coefficients and the data length of thedummy data are supplied to an additional frame generating section 2065(described later) and incorporated into an additional frame. Thebandwidth limitation processing section 2063 may change part of thequantization accuracy information, the number of quantization units,etc. that were changed by the bandwidth limitation processing section2063 in addition to part of the normalization coefficient informationand part of the spectrum coefficient information. The additional framegenerating section 2065 (described later) receives informationindicating the part of the quantization accuracy information, the numberof quantization units, etc. and incorporates these kinds of informationinto the additional frame.

Changing part of the normalization coefficient information and changingpart of the quantization accuracy information are much different fromeach other in the difficulty in inferring the original data illegally onthe basis of the trial listening data without using additional data,that is, in the safety of the trial listening data. For example, where abit allocation algorithm is employed in which quantization accuracyinformation is calculated on the basis of normalization coefficientinformation in generating original data, if part of only thequantization accuracy information is replaced by dummy data or “0,”there is a risk that the true quantization accuracy information isinferred successfully by using the normalization coefficientinformation.

In contrast, where part of only the normalization coefficientinformation is changed, it can be said that the safety of the triallistening data is high because it is difficult to infer the truenormalization coefficient information on the basis of the quantizationaccuracy information. Replacing both of part of the normalizationcoefficient information and part of the quantization accuracyinformation with dummy data or “0” further lowers the risk that theoriginal data are successfully inferred illegally. It is also possibleto selectively replace part of the normalization coefficient informationor part of the quantization accuracy information with dummy data or “0”from one content frame of the trial listening data to another.

The additional frame generating section 2065 generates, on the basis ofthe information relating to the normalization coefficient etc. that havebeen band-width-limited and modified by the bandwidth limitationprocessing section 2063, an additional frame to form additional data fororiginal data restoration that a user will buy to listen to a song withhigh sound quality after checking the trial listening data.

FIG. 46 shows a format of an additional frame that is generated in theabove manner. As described above with reference to FIG. 45, in the casewhere the quantization units [1] to [12] are selected as a triallistening band, in each frame of the trial listening data, thenormalization coefficients of the tone components and the non-tonecomponents in the four quantization units [13] to [16] are replaced by“0.” Part of the spectrum coefficient information that will not bereferred to are replaced by dummy data whose data length varies frame byframe. The additional frame generating section 2065 receives, from thebandwidth limitation processing section 2063, the original values of thechanged normalization coefficient information and spectrum coefficientinformation (i.e., true normalization coefficient information and truespectrum coefficient information) and information indicating the startposition of dummy data that replaced the spectrum coefficients and thedata length of the dummy data, and generates the additional frame ofFIG. 46.

Additional information corresponding to the tone components andadditional information corresponding to the non-tone components areincorporated in the additional frame. FIG. 46 shows a case that thequantization units [1] to [12] are selected as a trial listening band.The additional information corresponding to the tone components is thenumber of minimized tone components (in this example, two), thepositions, in the trial listening frame, of the normalizationcoefficient information of the minimized tone components, and the truenormalized coefficient information. The additional informationcorresponding to the non-tone components is the number of minimizednormalization coefficients of the non-tone components (in this example,four), the head positions of those normalization coefficients (e.g.,head quantization unit number “13” of the head of the quantization unitswhose normalization coefficients are changed to “0”), the truenormalization coefficients that are replaced, the position of thedummy-data-replaced portion of the true spectrum coefficientinformation, the dummy data bit length, and the true spectrumcoefficient information.

The position information of the dummy-data-replaced portion of the truespectrum coefficient information may not be included in the additionalframe, because it can be determined on the basis of the information ofthe regions of the quantization units whose normalization coefficientsare replaced by “0” if the dummy-data-replaced portion of the spectrumcoefficients is set, in the trial listening frame, at the head of thespectrum coefficient information that will not be referred to. Where thedummy-data-replaced portion of the spectrum coefficients is not set atthe head of the spectrum coefficient information that will not bereferred to, it is necessary to incorporate, in the additional frame,the position information of the dummy-data-replaced portion of the truespectrum coefficient information.

If, for example, the bandwidth limitation processing section 2063 haschanged quantization accuracy information, the number of quantizationunits, etc. in addition to part of the normalization coefficientinformation and part of the spectrum coefficient information, theadditional frame generating section 2065 receives information indicatingthe changed quantization accuracy information, the changed number ofquantization units, etc. and incorporates the true values of thesepieces of information into the additional frame.

The bandwidth limitation processing section 2063 generates the triallistening frame using such replacement data that the length of decodeddata to be obtained by decoding the trial listening data will not exceedthe length of decoded data to be obtained by decoding the original data.

A trial data generating section 2064 generates headers of the triallistening data, generates trial listening data by adding the generatedheaders to a coded frame sequence of received trial listening data, andoutputs the trial listening data. For example, the headers of the triallistening data contain a content ID for identification of the content, acontent reproduction time, a content title, information relating to acoding method, and other information.

An additional data generating section 2066 generates additional data byadding headers to a coded frame sequence of received additional data,and outputs the generated additional data. The headers of the additionaldata include such information as a content ID for identification of thecontent and association with the trial listening data, a contentreproduction time, and, if necessary, information relating to a codingmethod.

The original data can be restored by processing described later by usingthe trial listening data and the additional data that are generated bythe trial listening data generating section 2014 that was describedabove with reference to FIG. 42.

Next, a trial listening data generating process will be described withreference to a flowchart of FIG. 47.

At step S201, the trial listening data generation processing controlsection 2061 acquires a setting value of a trial listening band of triallistening data that is input from a manipulation input section (notshown) or the like. The following description will be made with anassumption that the quantization units [1] to [12] are set as a triallistening band as described above with reference to FIGS. 43 and 44. Thetrial listening data generation processing control section 2061 suppliesthe setting value of the trial listening band to the bandwidthlimitation processing section 2063.

At step S202, the bandwidth limitation processing section 2063 receivesa frame that is included in a frame sequence that corresponds tooriginal data.

At step S203, the bandwidth limitation processing section 2063 changes,to “0,” for example, the normalization coefficient information of thetone components of the received frame that are out of the band that isspecified by the setting value of the trial listening band that issupplied from the trial listening data generation processing controlsection 2061.

At step S204, the bandwidth limitation processing section 2063 changes,to “0,” for example, the normalization coefficient information of thenon-tone components that are out of the band that is specified by thesetting value of the trial listening band that is supplied from thetrial listening data generation processing control section 2061.

At step S2005, the random number generating section 2062 generates apseudo random number X and outputs it to the trial listening datageneration processing control section 2061. For example, pseudo randomnumbers X are generated by selecting a 100-bit arbitrary number first,squaring it, and selecting central 100 bits from the square (the lasttwo steps are repeated plural times (an arbitrary number of times)).

At step 206, the trial listening data generation processing controlsection 2061 determines a dummy data bit length R using the pseudorandom number X and supplies it to the bandwidth limitation processingsection 2063. For example, the trial listening data generationprocessing control section 2061 employs, as R, a remainder of the pseudorandom number X divided by 2^(n), where n is the number of bits ofspectrum coefficient information to be replaced by dummy data.Naturally, other methods of determining a dummy data bit length R may beused as long as they can generate a different numerical value each timein a range that is suitable for the number of bits of spectrumcoefficient information to be replaced by dummy data.

At step S207, the bandwidth limitation processing section 2063 generatesa trial listening frame as described above with reference to FIG. 45changes, by replacing those with random dummy data, spectrum coefficientinformation of R bits from a start position Ad among spectrumcoefficient information that corresponds to the normalizationcoefficient information of the non-tone components that was changed atstep S204 and will not be referred to, on the basis of the dummy databit length R that was determined at step S206 and is input from thetrial listening data generation processing control section 2061. Thebandwidth limitation processing section 2063 outputs the generated triallistening frame to the trial listening data generating section 2064, andoutputs the contents of the changes that were made at steps S203 to S207to the additional frame generating section 65.

The dummy data having the bit length R to replace spectrum coefficientinformation may have a value “0” in their entirety. Alternatively, 0sand 1s may be mixed with each other properly to make it difficult toidentify the dummy data. Where the spectrum coefficient information isvariable-length codes, an event that the frame length of the codesequence of the original data will be exceeded in decoding processing(described later) can be prevented by making a bit length that will beobtained when the dummy data are decoded smaller than a bit length thatwill be obtained when the true spectrum coefficient information isdecoded.

At step S208, on the basis of the signals that are input from thebandwidth limitation processing section 2063, the additional framegenerating section 2065 generates data for an additional frame toconstitute additional data that a user who will want to listen to a songwith high sound quality will buy after checking trial listening data(described above with reference to FIG. 46) and outputs the generateddata to the additional data generating section 2066.

At step S209, the trial listening data generation processing controlsection 2061 judges whether the frame just processed is the last frame.If it is judged at step S209 that the frame just processed is not thelast frame, the process returns to step S202 and step S202 and thesubsequent steps are executed again.

If it is judged at step S209 that the frame just processed is the lastframe, the process goes to step S210, where the trial listening datagenerating section 2064 generates headers for trial listening data,generates trial listening data by adding the headers to the triallistening frame sequence, and outputs the generated trial listeningdata.

At step S211, the additional data generating section 2066 generatesheaders for additional data by using the input information, generatesadditional data by adding the headers to the additional frame sequence,and outputs the generated additional data. The process is then finished.

The trial listening data to be reproduced with low quality and theadditional data to be used for restoring the original data from thetrial listening data are generated as a result of the execution of theprocess that is shown by the flowchart of FIG. 47.

As described above, the reproducible band of the trial listening datamay be restricted over the entire original data. Alternatively, tomotivate users who have received the trial listening data to buy thecontent more effectively, a prescribed portion of the trial listeningdata may be made reproducible with high sound quality like the originaldata. In this case, the portion is reproducible with high sound qualitylike the original data may be generated by copying corresponding framesof the original data into trial listening data as they are withoutperforming bandwidth limitation. It goes without saying that theadditional data do not include frames corresponding to the aboveportion.

It is also possible to make only a prescribed portion of the triallistening data bandwidth-limited data that are reproducible with lowquality and to make the other portions unreproducible. In this case, itis appropriate to replace, with dummy data, all the normalizationcoefficient information of frames corresponding to the unreproducibleportion and to incorporate all the true normalization coefficientinformation into additional frames.

In the above description, in coding an input signal, the signalcomponents coding section 2012 of the coding device 2001 separates tonecomponents and non-tone component from each other and codes the tonecomponents and the non-tone component separately. Alternatively, aninput signal may be coded without being divided into tone components andnon-tone components by employing the non-tone component coding section2033 shown in FIG. 40 instead of the signal component coding section2012.

FIG. 48 shows a format of an original data frame having high soundquality that is generated by the code sequence generating section 2013in the case where an input signal is not divided into tone componentsand non-tone components. As in the case of the format of FIG. 41, afixed-length header containing a sync signal is provided at the head ofthe original data frame. The number of bands of the band division filter2021 of the converting section 2011 that was described above withreference to FIG. 35 and other information are also incorporated in theheader. The number of quantization units (in this example, 16),quantization accuracy information of quantization that has beenperformed by the non-tone component coding section 2033, pieces ofnormalization coefficient information of the 16 respective quantizationunits, and spectrum coefficient information are arranged following theheader. A value “46” of the lowest-frequency quantization unit [1] to avalue “8” of the highest-frequency quantization unit [16] are arrangedas the normalization coefficient information for the respectivequantization units. Where the content frame length is fixed, an emptyregion may be provided after the spectrum coefficient information.

FIG. 49 shows a format of trial listening data that are generated by thetrial listening data generating section 2014 in response to the originaldata frame of FIG. 48. If quantization units [1] to [12], for example,are specified as a trial listening band, the values of the normalizationcoefficient information of the quantization units [13] to [16] that arehigher, in frequency, than the trial listening band are made “0”similarly in the case of the description with reference to FIG. 43.Dummy data whose data length varies frame by frame are incorporated asspectrum coefficient information of the quantization units [13] to [16].Therefore, it is very difficult to infer the original data from thetrial listening data.

FIG. 50 shows an additional frame that is generated by the additionalframe generating section 2065 of the trial listening data generatingsection 2014 in response to the original data frame of FIG. 48. Theadditional frame incorporates the number of minimized normalizationcoefficients (in this example, four), the head position of thosenormalization coefficients, the true normalization coefficients that arereplaced, the position of the dummy-data-replaced portion of the truespectrum coefficient information, the dummy data bit length that variesframe by frame, and the dummy-data-replaced portion of the true spectrumcoefficient information.

As described above with reference to FIGS. 48–50, low-quality triallistening data and additional data to be used for restoring the originaldata on the basis of the trial listening data are generated also in thecase where tone components are not separated from an input signal by theprocess that is similar to the process of the case that tone componentsare not separated from an input signal.

The trial listening data thus generated are delivered to users overInternet or distributed in such a manner as to be recorded on variousrecording media held by users by means of MMKs that are installed instored etc. If a user who has reproduced the trial listening data likesthe contents, he can acquire the additional data by paying a prescribedcharge to a content data delivery company. The user can restore theoriginal data using the trial listening data and the additional data,decode the original data, and reproduce or record on a recording mediumthe decoded original data.

Next, a description will be made of a process of decoding and outputtingor reproducing trial listening data or decoding and outputting orreproducing original data on the basis of trial listening data andadditional data.

FIG. 51 is a block diagram showing the configuration of a datareproducing device 2081.

A code sequence decomposing section 2091 receives coded trial listeningdata, decomposes the code sequence, extracts codes of respective signalcomponents, and output those to a code sequence restoring section 2093.

A control section 2092 receives manipulation input information, that is,information indicating whether to reproduce input data with high soundquality, of a user via a manipulation input section (not shown) and alsoreceives additional data, and controls the processing of the codesequence restoring section 2093. When necessary, the control section2092 supplies the code sequence restoring section 2093 with suchinformation as true normalization coefficient information, true spectrumcoefficient information, a position of spectrum coefficient information,and a dummy data bit length.

Controlled by the control section 2092, the code sequence restoringsection 2093 outputs the received coded frames to the signal componentdecoding section 2094 as they are if the input trial listening data areto be listened to, that is, reproduced as they are. If original data areto be restored from the input trial listening data and to be reproduced,the code sequence restoring section 2093 performs processing ofrestoring coded frames of original data from the coded frames of thetrial listening data on the basis of the various kinds of informationsuch as the true normalization coefficient information, the truespectrum coefficient information, the position of spectrum coefficientinformation, and the dummy data bit length that are supplied from thecontrol section 2092 and outputs the restored coded frames of theoriginal data to the signal component decoding section 2094.

The signal components decoding section 2094 decodes the received triallistening data or the coded frames of the original data. FIG. 52 is ablock diagram showing a detailed configuration of the signal componentdecoding section 2094 for decoding received coded frames that wereproduced after division into tone components and non-tone components.

A frame dividing section 2101 receives a coded frame as shown in FIG.45, for example, divides it into tone components and non-tonecomponents, and outputs the tone components and the non-tone componentsto a tone components decoding section 2102 and a non-tone componentsdecoding section 2103, respectively.

FIG. 53 is a block diagram showing a detailed configuration of the tonecomponents decoding section 2102. A dequantizing section 2111dequantizes received coded data and outputs dequantized coded data to ade-normalizing section 2112. The de-normalizing section 2112de-normalizes the received data. That is, the dequantizing section 2111and the de-normalizing section 2112 perform decoding processing andthereby produce spectrum signals of the tone components.

FIG. 54 is a block diagram showing a detailed configuration of thenon-tone components decoding section 2103. A dequantizing section 2121dequantizes received coded data and outputs dequantized coded data to ade-normalizing section 2122. The de-normalizing section 2122de-normalizes the received data. That is, the dequantizing section 2121and the de-normalizing section 2122 perform decoding processing andthereby produce spectrum signals of the non-tone components.

A spectrum signals combining section 2104 receives the spectrum signalsfrom the tone components decoding section 2102 and the non-tonecomponents decoding section 2103, combines those spectrum signals,generates spectrum signals as shown in FIG. 38 (original data) or FIG.44 (trial listening data), and outputs the generated spectrum signals tothe inverse converting section 2095.

Where coded data were produced without division into tone components andnon-tone components, decoding processing may be performed by omittingthe frame dividing section 2101 and using only one of the tonecomponents decoding section 2102 and the non-tone components decodingsection 2103.

FIG. 55 is a block diagram showing a detailed configuration of theinverse converting section 2095.

A signals dividing section 2131 divides the received signal on the basisof the number of bands (in this example, two) that is specified in theheader of the received frame. The signals dividing section 2131 dividesthe received spectrum signals into two parts, which are supplied toinverse spectrum converting sections 2132-1 and 2132-2, respectively.

The inverse spectrum converting sections 2132-1 and 2132-2 performinverse spectrum conversion on the received spectrum signals and outputresulting signals in the respective bands to a band combining filter2133. The band combining filter 2133 combines the received signals inthe respective bands and outputs a resulting signal.

The signal (e.g., an audio PCM signal) that is output from the bandcombining filter 2133 is converted by a D/A converter (not shown), forexample, into an analog signal, which is reproduced as sound by speakers(not shown). The signal that is output from the band combining filter2133 may be output to another apparatus over a network, for example.

Next, a data reproducing process that is executed by the datareproducing device 2081 of FIG. 51 will be described with reference to aflowchart of FIG. 56.

The code sequence decomposing section 2091 receives a coded frame oftrial listening data at step S31, and decomposes the received codesequence and outputs a decomposed code sequence to the code sequencerestoring section 2093 at step S32.

At step S33, the code sequence restoring section 2093 judges, on thebasis of a signal that is input from the control section 2092, whetherhigh-sound-quality reproduction, that is, processing of restoring andreproducing original data, should be performed.

If it is judged at step S33 that high-sound-quality reproduction shouldbe performed, the process goes to step S34, where a code sequencerestoring process (described later with reference to a flowchart of FIG.57) is executed.

If it is judged at step S33 that high-sound-quality reproduction shouldnot be performed or if step S34 is executed, the process goes to stepS35, where the signal components decoding section 2094 divides areceived code sequence into tone components and non-tone components, anddecodes the tone components and the non-tone components individually bydequantizing and de-normalizing those, combines resulting spectrumsignals, and outputs combined spectrum signals to the inverse convertingsection 2095.

At step S36, the inverse converting section 2095 divides the receivedspectrum signals into bands if necessary, performs inverse spectrumconversion in the respective bands, performs band combining, and finallyperforms inverse conversion into a time-series signal.

At step S37, the control section 2092 judges whether the frame that hasbeen inverse-converted by the inverse converting section 2095 at stepS36 is the last frame of the trial listening data.

If it is judged at step S37 that the frame concerned is not the lastframe, the process returns to step S31 and step S31 and the subsequentsteps are executed again. If it is judged at step S37 that the frameconcerned is the last frame, the process is finished.

The time-series signal generated by the inverse converting section 2095by the inverse conversion may be converted into an analog signal by aD/A converting section (not shown) and then reproduced by speakers (notshown) or output to another apparatus or the like over a network (notshown).

Although above description is directed to the case of decoding triallistening data that were coded after division into tone components andnon-tone components or original data that have been restored from suchtrial listening data, restoring processing and reproduction processingcan be performed in a similar manner also in the case where triallistening data were coded without division into tone components andnon-tone components.

Next, the code sequence restoring process that is executed at step S34in FIG. 56 will be described with reference to a flowchart of FIG. 57.

At step S51, to restore a code sequence, the code sequence restoringsection 2093 acquires, from the control section 2092, additional datasuch as true normalization coefficient information, true spectrumcoefficient information, a position of spectrum coefficient information,and a dummy data bit length.

At step S52, the code sequence restoring section 2093 receives a framethat has been decomposed by the code sequence decomposing section 2091.

At step S53, the code sequence restoring section 2093 replaces 0-valuenormalization coefficient information of tone components in the triallistening frame of the trial listening data with the true normalizationcoefficient information of the tone components that is contained in theadditional frame (see FIG. 46).

At step S54, the code sequence restoring section 2093 replaces 0-valuenormalization coefficient information of non-tone components in thetrial listening frame of the trial listening data with the truenormalization coefficient information of the non-tone components that iscontained in the additional frame (see FIG. 46).

At step S55, the code sequence restoring section 2093 reads the dummydata bit length R and the start position Ad from the additional frame(see FIG. 46).

At step S56, the code sequence restoring section 2093 replacesdummy-data spectrum coefficient information of the non-tone componentsthat starts from the position Ad in the trial listening frame of thetrial listening data and has the bit length R with the true spectrumcoefficient information of the non-tone components that is contained inthe additional frame (see FIG. 46). Then, a return is made to step S35in FIG. 56.

Original data are restored on the basis of the trial listening data andthe additional data by the process that has been described above withreference to the flowchart of FIG. 57.

The trial listening data decoded or the original data restored anddecoded by the process that has been described above with reference toFIGS. 51–57 may be reproduced by speakers (not shown) or the like oroutput to another apparatus over a network or the like.

Next, a description will be made of a process of recording triallistening data on a recording medium, or restoring original data fromtrial listening data and additional data and recording the original dataon a recording medium.

FIG. 58 is a block diagram showing the configuration of a data recordingdevice 2141.

The sections in FIG. 58 having the corresponding sections of the datareproducing device 2081 in FIG. 51 are given the same reference numeralsas the latter and will not be described if appropriate.

A code sequence decomposing section 2091 receives coded trial listeningdata and extracts codes of respective signal components by decomposingthe code sequence. A control section 2092 receives, from a user, via amanipulation input section (not shown), manipulation input information,that is, information indicating whether to record the received data withhigh sound quality (i.e., whether to perform processing of restoring andrecording original data). The control section 2092 also receivesadditional data and controls the processing of a code sequence restoringsection 2093.

Controlled by the control section 2092, the code sequence restoringsection 2093 outputs the received coded frames to the recording section2151 as they are if the input trial listening data are to be recorded asthey are. If original data are to be restored and recorded, the codesequence restoring section 2093 performs processing of restoring codedframes of original data from the received trial listening data on thebasis of various kinds of information such as true normalizationcoefficient information, true spectrum coefficient information, aposition of spectrum coefficient information, and a dummy data bitlength that are supplied from the control section 2092 and outputs therestored coded frames of the original data to the recording section2151.

The recording section 2151 records data on a recording medium such as amagnetic disk, an optical disc, a magneto-optical disc, a semiconductormemory, or a magnetic tape by a prescribed method. The recording section2151 may be such as to record information inside the device, such as amemory provided on a circuit board or a hard disk drive. For example,where the recording section 2151 is such as to be able to record data onan optical disc, the recording section 2151 is composed of an encoderfor converting data into a format that is suitable for recording on theoptical disc, an optical unit consisting of a laser light source such asa laser diode, various lenses, a polarizing beam splitter, etc., aspindle motor for rotating the optical disc, a driving section fordriving the optical unit so as to move it to a prescribed trackposition, a control section for controlling the above components, etc.

The recording medium to be mounted in the recording section 2151 may bethe same recording medium as trial listening data to be input to thecode sequence decomposing section 2091 or additional data to be input tothe control section 2092 are recorded on.

Next, a data recording process that is executed by the data recordingdevice 2141 will be described with reference to a flowchart of FIG. 59.

Steps S81 to S84 are the same as steps S31 to S34 in FIG. 56,respectively.

The code sequence decomposing section 2091 receives a coded frame oftrial listening data at step S81, and decomposes the received codesequence and outputs a decomposed code sequence to the code sequencerestoring section 2093 at step S82.

At step S83, the code sequence restoring section 2093 judges, on thebasis of a signal that is input from the control section 2092, whetherhigh-sound-quality reproduction should be performed. If it is judged atstep S83 that high-sound-quality reproduction should be performed, theprocess goes to step S84, where the code sequence restoring process(described above with reference to the flowchart of FIG. 57) isexecuted.

If it is judged at step S83 that high-sound-quality reproduction shouldnot be performed or if step S84 is executed, the process goes to stepS85, where the recording section 2151 records a frame of receivedoriginal data or a code sequence corresponding to the trial listeningdata on, for example, a recording medium mounted therein.

At step S86, the control section 2092 judges what was recorded on therecording medium by the recording section 2151 at step S85 is the lastframe of the original data or the code sequence corresponding to thetrial listening data.

If it is judged at step S86 that the frame concerned is not the lastframe, the process returns to step S81 and step S81 and the subsequentsteps are executed again. If it is judged at step S86 that the frameconcerned is the last frame, the process is finished.

According to the second embodiment of the invention, trial listeningdata can be generated by changing the values of or replacing with dummydata normalization coefficient information and variable-length-codedspectrum coefficient information. Information in regions that do notaffect reproduction sound during reproduction of trial listening data isreplaced by dummy data. An example of the regions that do not affectreproduction sound during reproduction of trial listening data is aregion where spectrum coefficient information exists that corresponds toa region where normalization coefficient information is replaced by “0.”The bit length of dummy data to replace spectrum coefficient informationis varied frame by frame.

It is very difficult to infer original data from such trial listeningdata. Where spectrum coefficient information is variable-length codes,inferring original data from trial listening data is even moredifficult. Illegally altering trial listening data may deteriorate thesound quality on the contrary. Therefore, the rights of an author and amarketer of contents can be protected.

Additional data are generated that consist of additional framecontaining true values of data that are changed or replaced by dummydata in generating trial listening data (e.g., true normalizationcoefficient information, true spectrum coefficient information, truequantization accuracy information, and the number of quantization units)and dummy data bit lengths of respective frames. Therefore, originaldata can be restored from the trial listening data by using theadditional data.

The second embodiment of the invention makes it possible to reproducerestored original data, to record restored original data on a recordingmedium, and to output restored original data to another apparatus over anetwork or the like.

The above description is directed to the process of generating triallistening data of audio signal contents data and correspondingadditional data, or restoring original data on the basis of triallistening data and additional data and reproducing or recording therestored original data. However, the invention can also be applied tocontents data that consist of an image signal or an image signal and anaudio signal.

For example, where image signal contents data are converted bytwo-dimensional DCT and quantized by using various quantization tables,trial listening data are generated by designating a dummy quantizationtable in which high-frequency components are removed and incorporatingdummy data whose data length varies frame by frame into a region of ahigh-frequency portion of spectrum coefficient information. Thehigh-frequency components that are removed from the quantization tableand the dummy-data-replaced portion of the spectrum coefficientinformation are incorporated in additional data.

In restoring original data, a true quantization table having thehigh-frequency components and true spectrum coefficient information arerestored by using the additional data. The original data can thus berestored and reproduced.

The second embodiment of the invention can be applied to the case thatit is intended to prevent a third person from restoring original dataeasily by changing part of variable-length codes of not only contentsdata and framed data but also other various data. That is, data that arelower in quality than original data can be generated by replacing pluralportions of variable-length codes with dummy data and varying the dummydata length dummy data by dummy data. Original data cannot be restoredeasily from the low-quality data irrespective of the type of originaldata.

The above-described first and second embodiments may be practiced notonly solely but also in proper combination. That is, the invention canbe practiced by properly combining the methods or configurationsdescribed in this specification and other methods or configurations inaccordance with an intended form of practice. Such implementations areconstrued as being covered by the technical scope of the invention asdefined by the claims and equivalents thereof.

The above-described processes according to the first and secondembodiments can be executed either hardware or software. To this end,each of the coding device 2001, the data reproducing device 2081, andthe data recording device 2141, for example, takes the form of apersonal computer 2161 shown in FIG. 60.

In FIG. 60, a CPU 2171 performs various kinds of processing according toa program that is stored in a ROM 2172 or has been loaded into a RAM2173 from the storing section 2178. Data necessary for the CPU 2171 toperform various kinds of processing are also stored in the RAM 2173 asappropriate.

The CPU 2171, the ROM 2172, and the RAM 2173 are connected to each othervia a bus 2174. An input/output interface 2175 is also connected to thebus 2174.

An input section 2176 such as a key board and a mouse, an output section2177 such as a display, a storing section 2178 such as a hard diskdrive, and a communication section 2179 such as a modem or a terminaladapter are connected to the input/output interface 2175. Thecommunication section 2179 performs communication processing via anetwork such as the Internet.

A drive 2180 is connected to the input/output interface 2175 ifnecessary, and a magnetic disk 2191, an optical disc 2192, amagneto-optical disc 2193, a semiconductor memory 2194, or the like ismounted in the drive 2180 as desired. A computer program read from sucha disc, memory, or the like is installed in the storing section 2178 ifnecessary.

Where the above-described processes are executed by software, programsconstituting the software are installed, via a network or a recordingmedium, in a computer that is incorporated in dedicated hardware or ageneral-purpose personal computer, for example, capable of performingvarious functions when various programs are installed therein.

As shown in FIG. 60, this recording medium may be either aprograms-stored package medium that is separate from the apparatus mainbody and is distributed to a user to supply programs to him such as themagnetic disk 2191 (including a floppy disk), optical disc 2192(including a CD-ROM (compact disc-read only memory and a DVD (digitalversatile disc)), magneto-optical disc 2193 (including an MD (mini-disc;trademark)), or semiconductor memory 2194, or a recording medium that issupplied to a user in a state that it is incorporated in the apparatusmain body such as the ROM 2172 in which programs are stored or a harddisk drive that is incorporated in the storing section 2178.

In this specification, the steps of a program that is recorded in arecording medium may naturally be executed in time-series order, i.e.,in written order. However, they may not necessarily be executed intime-series order; they may be executed in parallel or individually.

In the signal reproducing method and device and the signal recordingdevice and method according to the invention, to reproduce or record acode sequence obtained by coding a signal in units of a frame, adummy-data-replaced portion of a first code sequence is replaced by truedata by using a second code sequence containing information that isnecessary for dummy data replacement (and a resulting code sequence isdecoded). In the first code sequence, the position of the dummy datavaries. Therefore, inferring trial viewing data containing the firstcode sequence is made very difficult while the size of high qualityrestoration data is relatively small, whereby the safety of the trialviewing data is increased.

According to the invention, a first code sequence obtained by replacingpart of a code sequence with dummy data is used as trial viewing dataand, if a second code sequence containing information necessary fordummy data replacement is input, at least part of the dummy data portionof the first code sequence is replaced by using the second codesequence. An empty region of the first code sequence is filled with arandom pseudo-code sequence. When someone attempts to illegally increasethe quality (e.g., bandwidth) of the first code sequence (trial viewingdata), it is difficult for him to judge whether a resulting codesequence is a correct one. As a result, illegal high quality restorationcan be prevented and the safety of trial viewing data (first codesequence) can be increased.

In the code sequence generating method and device according to theinvention, to generate a code sequence obtained by coding a signal inprescribed units, a first code sequence is generated in which part ofthe above code sequence is replaced by dummy data and a second codesequence is also generated that contains information necessary forreplacement of at least part of the dummy data. An empty region of thefirst code sequence is filled with a random pseudo-code sequence. Whensomeone attempts to illegally increase the quality (e.g., bandwidth) ofthe first code sequence that is supplied as trial viewing data, it isdifficult for him to judge whether a resulting code sequence is acorrect one. As a result, illegal high quality restoration can beprevented and the safety of trial viewing data can be increased.

Further, the invention makes it possible to convert a data sequence.

According to the invention, an original data sequence, for example, canbe converted into a data sequence such as trial listening data fromwhich the original data sequence is hard to infer and another datasequence such as additional data that is necessary for restoring theoriginal data sequence from the data sequence obtained by the aboveconversion can be generated. Varying, frame by frame, the data length ofdummy data to be replaced by true data makes it more difficult to inferthe original data sequence from the data sequence obtained by the aboveconversion.

Further, the invention makes it possible to restore a data sequence.

According to the invention, an original data sequence can be restoredfrom a data sequence such as trial listening data by separatelyacquiring another data sequence such as additional data to be used forrestoring the former data sequence.

The invention makes it possible to distribute very safe trial listeningdata to users.

Still further, the invention makes it possible to restore original datafrom trial listening data.

1. A signal reproducing method for reproducing a code sequence obtainedby coding a signal in prescribed units, comprising: a first codesequence receiving step of receiving a first code sequence obtained byreplacing part of the code sequence with dummy data; a replacing step ofreplacing, if a second code sequence containing information necessaryfor dummy data replacement is received, at least part of the dummy dataof the first code sequence with true data by using the second codesequence; and a decoding step of decoding the first code sequence or acode sequence obtained by the replacing step, wherein in the first codesequence the dummy data are located at a position that is variable inthe prescribed units.
 2. The signal reproducing method according toclaim 1, wherein the dummy data are provided in the first code sequencein the prescribed units.
 3. The signal reproducing method according toclaim 1, wherein a head position of the dummy data in the first codesequence varies in the prescribed units.
 4. The signal reproducingmethod according to claim 1, wherein the code sequence containsvariable-length codes, and wherein at least part of the dummy datacorrespond to variable-length codes.
 5. The signal reproducing methodaccording to claim 1, wherein the code sequence is generated by codingthe signal in such a manner that the signal is spectrum-converted anddivided into bands, and a code sequence having a prescribed format isgenerated that contains quantization accuracy information, normalizationcoefficient information, and spectrum coefficient information in eachband, and wherein the dummy data include dummy data that correspond toat least part of the spectrum coefficient information.
 6. The signalreproducing method according to claim 5, wherein the spectrumcoefficient information is variable-length codes, and wherein afterconverted into variable-length codes the dummy data of the first codesequence are not longer than coded data of original data.
 7. A signalreproducing device for reproducing a code sequence obtained by coding asignal in prescribed units, comprising: first code sequence receivingmeans for receiving a first code sequence obtained by replacing part ofthe code sequence with dummy data; replacing means for replacing, if asecond code sequence containing information necessary for dummy datareplacement is received, at least part of the dummy data of the firstcode sequence with true data by using the second code sequence; anddecoding means for decoding the first code sequence or a code sequenceobtained by the replacing means, wherein in the first code sequence thedummy data are located at a position that is variable in the prescribedunits.
 8. The signal reproducing device according to claim 7, whereinthe dummy data are provided in the first code sequence in the prescribedunits.
 9. The signal reproducing device according to claim 7, wherein ahead position of the dummy data in the first code sequence varies in theprescribed units.
 10. The signal reproducing device according to claim7, wherein the code sequence is generated by coding the signal in such amanner that the signal is spectrum-converted and divided into bands, anda code sequence having a prescribed format is generated that containsquantization accuracy information, normalization coefficientinformation, and spectrum coefficient information in each band, andwherein the dummy data include dummy data that correspond to at leastpart of the spectrum coefficient information.
 11. The signal reproducingdevice according to claim 10, wherein the spectrum coefficientinformation is variable-length codes, and wherein after converted intovariable-length codes the dummy data of the first code sequence are notlonger than coded data of original data.
 12. A signal recording methodfor recording, on a recording medium, a code sequence obtained by codinga signal in prescribed units, comprising: a first code sequencereceiving step of receiving a first code sequence obtained by replacingpart of the code sequence with dummy data; and a replacing step ofreplacing, if a second code sequence containing information necessaryfor dummy data replacement is received, at least part of the dummy dataof the first code sequence with true data by using the second codesequence, wherein in the first code sequence the dummy data are locatedat a position that is variable in the prescribed units.
 13. The signalrecording method according to claim 12, wherein the dummy data areprovided in the first code sequence in the prescribed units.
 14. Thesignal recording method according to claim 12, wherein a head positionof the dummy data in the first code sequence varies in the prescribedunits.
 15. The signal recording method according to claim 12, whereinthe code sequence is generated by coding the signal in such a mannerthat the signal is spectrum-converted and divided into bands, and a codesequence having a prescribed format is generated that containsquantization accuracy information, normalization coefficientinformation, and spectrum coefficient information in each band, andwherein the dummy data include dummy data that correspond to at leastpart of the spectrum coefficient information.
 16. The signal recordingmethod according to claim 15, wherein the spectrum coefficientinformation is variable-length codes, and wherein after converted intovariable-length codes the dummy data of the first code sequence are notlonger than coded data of original data.
 17. A signal recording devicefor recording, on a recording medium, a code sequence obtained by codinga signal in prescribed units, comprising: first code sequence receivingmeans for receiving a first code sequence obtained by replacing part ofthe code sequence with dummy data; and replacing means for replacing, ifa second code sequence containing information necessary for dummy datareplacement is received, at least part of the dummy data of the firstcode sequence with true data by using the second code sequence, whereinin the first code sequence the dummy data are located at a position thatis variable in the prescribed units.
 18. The signal recording deviceaccording to claim 17, wherein the dummy data are provided in the firstcode sequence in the prescribed units.
 19. The signal recording deviceaccording to claim 17, wherein a head position of the dummy data in thefirst code sequence varies in the prescribed units.
 20. The signalrecording device according to claim 17, wherein the code sequence isgenerated by coding the signal in such a manner that the signal isspectrum-converted and divided into bands, and a code sequence having aprescribed format is generated that contains quantization accuracyinformation, normalization coefficient information, and spectrumcoefficient information in each band, and wherein the dummy data includedummy data that correspond to at least part of the spectrum coefficientinformation.
 21. The signal recording device according to claim 20,wherein the spectrum coefficient information is variable-length codes,and wherein after converted into variable-length codes the dummy data ofthe first code sequence are not longer than coded data of original data.22. A code sequence generating method comprising: a coding step ofgenerating a code sequence of a prescribed format by coding an inputsignal; a first code sequence generating step of generating a first codesequence by replacing part of the code sequence of the prescribed formatwith dummy data; and a second code sequence generating step ofgenerating a second code sequence by extracting the part of codesequence of the prescribed format corresponding to the dummy data,wherein in the first code sequence the dummy data are located at aposition that is variable in prescribed units.
 23. The code sequencegenerating method according to claim 22, wherein the dummy data areprovided in the first code sequence in the prescribed units.
 24. Thecode sequence generating method according to claim 22, wherein a headposition of the dummy data in the first code sequence varies in theprescribed units.
 25. The code sequence generating method according toclaim 22, wherein the code sequence contains variable-length codes, andwherein at least part of the dummy data correspond to variable-lengthcodes.
 26. The code sequence generating method according to claim 22,wherein the coding step spectrum-converts and divides into bands theinput signal, and generates a code sequence having the prescribed formatthat contains quantization accuracy information, normalizationcoefficient information, and spectrum coefficient information in eachband, and wherein the dummy data include dummy data that correspond toat least part of the spectrum coefficient information.
 27. The codesequence generating method according to claim 26, wherein the spectrumcoefficient information is variable-length codes, and wherein afterconverted into variable-length codes the dummy data of the first codesequence are not longer than coded data of original data.
 28. A codesequence generating device comprising: coding means for generating acode sequence of a prescribed format by coding an input signal; firstcode sequence generating means for generating a first code sequence byreplacing part of the code sequence of the prescribed format with dummydata; and second code sequence generating means for generating a secondcode sequence by extracting the part of code sequence of the prescribedformat corresponding to the dummy data, wherein in the first codesequence the dummy data are located at a position that is variable inprescribed units.
 29. The code sequence generating device according toclaim 28, wherein the dummy data are provided in the first code sequencein the prescribed units.
 30. The code sequence generating deviceaccording to claim 28, wherein a head position of the dummy data in thefirst code sequence varies in the prescribed units.
 31. The codesequence generating device according to claim 28, wherein the codesequence contains variable-length codes, and wherein at least part ofthe dummy data correspond to variable-length codes.
 32. The codesequence generating device according to claim 28, wherein the codingmeans spectrum-converts and divides into bands the input signal, andgenerates a code sequence having the prescribed format that containsquantization accuracy information, normalization coefficientinformation, and spectrum coefficient information in each band, andwherein the dummy data include dummy data that correspond to at leastpart of the spectrum coefficient information.
 33. The code sequencegenerating device according to claim 32, wherein the spectrumcoefficient information is variable-length codes, and wherein afterconverted into variable-length codes the dummy data of the first codesequence are not longer than coded data of original data.